From 363045886d499de653cbab1f9fd9678d72ba5da2 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 30 Jun 2023 13:05:11 -0700
Subject: [PATCH 01/17] Impl

---
 runtime/runtime_controller.cc                 |  4 +-
 .../Headers/FlutterPluginRegistrarMacOS.h     |  4 +-
 .../framework/Source/FlutterCompositor.mm     |  2 +-
 .../framework/Source/FlutterCompositorTest.mm | 18 ++++-----
 .../macos/framework/Source/FlutterEngine.mm   | 38 +++++++++----------
 .../framework/Source/FlutterEngineTest.mm     |  6 +--
 .../framework/Source/FlutterEngine_Internal.h |  8 ++--
 .../macos/framework/Source/FlutterView.h      |  2 +-
 .../Source/FlutterViewEngineProviderTest.mm   |  2 +-
 .../macos/framework/Source/FlutterViewTest.mm |  4 +-
 10 files changed, 43 insertions(+), 45 deletions(-)

diff --git a/runtime/runtime_controller.cc b/runtime/runtime_controller.cc
index 5ffd02d099139..4837c5946c532 100644
--- a/runtime/runtime_controller.cc
+++ b/runtime/runtime_controller.cc
@@ -20,7 +20,7 @@
 
 namespace flutter {
 
-const uint64_t kFlutterDefaultViewId = 0llu;
+const uint64_t kFlutterImplicitViewId = 0llu;
 
 RuntimeController::RuntimeController(RuntimeDelegate& p_client,
                                      const TaskRunners& task_runners)
@@ -320,7 +320,7 @@ void RuntimeController::ScheduleFrame() {
 // |PlatformConfigurationClient|
 void RuntimeController::Render(Scene* scene) {
   // TODO(dkwingsmt): Currently only supports a single window.
-  int64_t view_id = kFlutterDefaultViewId;
+  int64_t view_id = kFlutterImplicitViewId;
   auto window =
       UIDartState::Current()->platform_configuration()->get_window(view_id);
   if (window == nullptr) {
diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index 8e99ad83eba3f..0a5ae5dd695a8 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -36,11 +36,9 @@ FLUTTER_DARWIN_EXPORT
 @property(nonnull, readonly) id<FlutterTextureRegistry> textures;
 
 /**
- * The default view displaying Flutter content.
+ * The view displaying Flutter content.
  *
  * This method may return |nil|, for instance in a headless environment.
- *
- * The default view is a special view operated by single-view APIs.
  */
 @property(nullable, readonly) NSView* view;
 
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm b/shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm
index 3da1c44edf0c4..b40234c5b3bc8 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm
@@ -22,7 +22,7 @@
   // TODO(dkwingsmt): This class only supports single-view for now. As more
   // classes are gradually converted to multi-view, it should get the view ID
   // from somewhere.
-  FlutterView* view = [view_provider_ viewForId:kFlutterDefaultViewId];
+  FlutterView* view = [view_provider_ viewForId:kFlutterImplicitViewId];
   if (!view) {
     return false;
   }
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterCompositorTest.mm b/shell/platform/darwin/macos/framework/Source/FlutterCompositorTest.mm
index f7ac37e01be68..081c3e22e86eb 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterCompositorTest.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterCompositorTest.mm
@@ -12,27 +12,27 @@
 #import "flutter/testing/testing.h"
 
 @interface FlutterViewMockProvider : NSObject <FlutterViewProvider> {
-  FlutterView* _defaultView;
+  FlutterView* _implicitView;
 }
 /**
- * Create a FlutterViewMockProvider with the provided view as the default view.
+ * Create a FlutterViewMockProvider with the provided view as the implicit view.
  */
-- (nonnull instancetype)initWithDefaultView:(nonnull FlutterView*)view;
+- (nonnull instancetype)initWithImplicitView:(nonnull FlutterView*)view;
 @end
 
 @implementation FlutterViewMockProvider
 
-- (nonnull instancetype)initWithDefaultView:(nonnull FlutterView*)view {
+- (nonnull instancetype)initWithImplicitView:(nonnull FlutterView*)view {
   self = [super init];
   if (self != nil) {
-    _defaultView = view;
+    _implicitView = view;
   }
   return self;
 }
 
 - (nullable FlutterView*)viewForId:(FlutterViewId)viewId {
-  if (viewId == kFlutterDefaultViewId) {
-    return _defaultView;
+  if (viewId == kFlutterImplicitViewId) {
+    return _implicitView;
   }
   return nil;
 }
@@ -81,7 +81,7 @@ - (nullable FlutterView*)viewForId:(FlutterViewId)viewId {
 
   OCMStub([surfaceMock asFlutterMetalTexture]).andReturn(texture);
 
-  return [[FlutterViewMockProvider alloc] initWithDefaultView:viewMock];
+  return [[FlutterViewMockProvider alloc] initWithImplicitView:viewMock];
 }
 }  // namespace
 
@@ -131,7 +131,7 @@ - (nullable FlutterView*)viewForId:(FlutterViewId)viewId {
   }};
   const FlutterLayer* layers_ptr = layers;
 
-  macos_compositor->Present(kFlutterDefaultViewId, &layers_ptr, 1);
+  macos_compositor->Present(kFlutterImplicitViewId, &layers_ptr, 1);
 
   ASSERT_EQ(presentedSurfaces.count, 1ul);
 }
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm b/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
index 138ebdc1c6be7..caab9c1852d53 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
@@ -95,7 +95,7 @@ - (nullable FlutterViewController*)viewControllerForId:(FlutterViewId)viewId;
  * An internal method that adds the view controller with the given ID.
  *
  * This method assigns the controller with the ID, puts the controller into the
- * map, and does assertions related to the default view ID.
+ * map, and does assertions related to the implicit view ID.
  */
 - (void)registerViewController:(FlutterViewController*)controller forId:(FlutterViewId)viewId;
 
@@ -296,7 +296,7 @@ - (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine
 }
 
 - (NSView*)view {
-  return [self viewForId:kFlutterDefaultViewId];
+  return [self viewForId:kFlutterImplicitViewId];
 }
 
 - (NSView*)viewForId:(FlutterViewId)viewId {
@@ -422,9 +422,9 @@ - (instancetype)initWithName:(NSString*)labelPrefix
   [_isResponseValid addObject:@YES];
   _terminationHandler = [[FlutterEngineTerminationHandler alloc] initWithEngine:self
                                                                      terminator:nil];
-  // kFlutterDefaultViewId is reserved for the default view.
+  // kFlutterImplicitViewId is reserved for the implicit view.
   // All IDs above it are for regular views.
-  _nextViewId = kFlutterDefaultViewId + 1;
+  _nextViewId = kFlutterImplicitViewId + 1;
 
   _embedderAPI.struct_size = sizeof(FlutterEngineProcTable);
   FlutterEngineGetProcAddresses(&_embedderAPI);
@@ -506,10 +506,10 @@ - (BOOL)runWithEntrypoint:(NSString*)entrypoint {
   flutterArguments.update_semantics_callback2 = [](const FlutterSemanticsUpdate2* update,
                                                    void* user_data) {
     // TODO(dkwingsmt): This callback only supports single-view, therefore it
-    // only operates on the default view. To support multi-view, we need a
+    // only operates on the implicit view. To support multi-view, we need a
     // way to pass in the ID (probably through FlutterSemanticsUpdate).
     FlutterEngine* engine = (__bridge FlutterEngine*)user_data;
-    [[engine viewControllerForId:kFlutterDefaultViewId] updateSemantics:update];
+    [[engine viewControllerForId:kFlutterImplicitViewId] updateSemantics:update];
   };
   flutterArguments.custom_dart_entrypoint = entrypoint.UTF8String;
   flutterArguments.shutdown_dart_vm_when_done = true;
@@ -645,7 +645,7 @@ - (FlutterViewController*)viewControllerForId:(FlutterViewId)viewId {
 
 - (void)setViewController:(FlutterViewController*)controller {
   FlutterViewController* currentController =
-      [_viewControllers objectForKey:@(kFlutterDefaultViewId)];
+      [_viewControllers objectForKey:@(kFlutterImplicitViewId)];
   if (currentController == controller) {
     // From nil to nil, or from non-nil to the same controller.
     return;
@@ -658,26 +658,26 @@ - (void)setViewController:(FlutterViewController*)controller {
              @"If you wanted to create an FlutterViewController and set it to an existing engine, "
              @"you should use FlutterViewController#init(engine:, nibName, bundle:) instead.",
              controller.engine);
-    [self registerViewController:controller forId:kFlutterDefaultViewId];
+    [self registerViewController:controller forId:kFlutterImplicitViewId];
   } else if (currentController != nil && controller == nil) {
-    NSAssert(currentController.viewId == kFlutterDefaultViewId,
+    NSAssert(currentController.viewId == kFlutterImplicitViewId,
              @"The default controller has an unexpected ID %llu", currentController.viewId);
     // From non-nil to nil.
-    [self deregisterViewControllerForId:kFlutterDefaultViewId];
+    [self deregisterViewControllerForId:kFlutterImplicitViewId];
     [self shutDownIfNeeded];
   } else {
     // From non-nil to a different non-nil view controller.
     NSAssert(NO,
              @"Failed to set view controller to the engine: "
-             @"The engine already has a default view controller %@. "
-             @"If you wanted to make the default view render in a different window, "
+             @"The engine already has an implicit view controller %@. "
+             @"If you wanted to make the implicit view render in a different window, "
              @"you should attach the current view controller to the window instead.",
-             [_viewControllers objectForKey:@(kFlutterDefaultViewId)]);
+             [_viewControllers objectForKey:@(kFlutterImplicitViewId)]);
   }
 }
 
 - (FlutterViewController*)viewController {
-  return [self viewControllerForId:kFlutterDefaultViewId];
+  return [self viewControllerForId:kFlutterImplicitViewId];
 }
 
 - (FlutterCompositor*)createFlutterCompositor {
@@ -705,9 +705,9 @@ - (FlutterCompositor*)createFlutterCompositor {
                                            void* user_data               //
                                         ) {
     // TODO(dkwingsmt): This callback only supports single-view, therefore it
-    // only operates on the default view. To support multi-view, we need a new
+    // only operates on the implicit view. To support multi-view, we need a new
     // callback that also receives a view ID.
-    return reinterpret_cast<flutter::FlutterCompositor*>(user_data)->Present(kFlutterDefaultViewId,
+    return reinterpret_cast<flutter::FlutterCompositor*>(user_data)->Present(kFlutterImplicitViewId,
                                                                              layers, layers_count);
   };
 
@@ -725,7 +725,7 @@ - (FlutterCompositor*)createFlutterCompositor {
 #pragma mark - Framework-internal methods
 
 - (void)addViewController:(FlutterViewController*)controller {
-  [self registerViewController:controller forId:kFlutterDefaultViewId];
+  [self registerViewController:controller forId:kFlutterImplicitViewId];
 }
 
 - (void)removeViewController:(nonnull FlutterViewController*)viewController {
@@ -812,7 +812,7 @@ - (nonnull NSString*)executableName {
 }
 
 - (void)updateWindowMetricsForViewController:(FlutterViewController*)viewController {
-  if (viewController.viewId != kFlutterDefaultViewId) {
+  if (viewController.viewId != kFlutterImplicitViewId) {
     // TODO(dkwingsmt): The embedder API only supports single-view for now. As
     // embedder APIs are converted to multi-view, this method should support any
     // views.
@@ -1078,7 +1078,7 @@ - (void)handleAccessibilityEvent:(NSDictionary<NSString*, id>*)annotatedEvent {
 - (void)announceAccessibilityMessage:(NSString*)message
                         withPriority:(NSAccessibilityPriorityLevel)priority {
   NSAccessibilityPostNotificationWithUserInfo(
-      [self viewControllerForId:kFlutterDefaultViewId].flutterView,
+      [self viewControllerForId:kFlutterImplicitViewId].flutterView,
       NSAccessibilityAnnouncementRequestedNotification,
       @{NSAccessibilityAnnouncementKey : message, NSAccessibilityPriorityKey : @(priority)});
 }
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterEngineTest.mm b/shell/platform/darwin/macos/framework/Source/FlutterEngineTest.mm
index 60e8bc363f8df..4fccfa0dedc9b 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterEngineTest.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterEngineTest.mm
@@ -25,7 +25,7 @@
 // CREATE_NATIVE_ENTRY and MOCK_ENGINE_PROC are leaky by design
 // NOLINTBEGIN(clang-analyzer-core.StackAddressEscape)
 
-constexpr int64_t kDefaultViewId = 0ll;
+constexpr int64_t kImplicitViewId = 0ll;
 
 @interface FlutterEngine (Test)
 /**
@@ -354,7 +354,7 @@ - (nonnull NSView*)createWithViewIdentifier:(int64_t)viewId arguments:(nullable
   FlutterSemanticsNode2* nodes[] = {&root, &child1};
   update.nodes = nodes;
   update.custom_action_count = 0;
-  // This call updates semantics for the default view, which does not exist,
+  // This call updates semantics for the implicit view, which does not exist,
   // and therefore this call is invalid. But the engine should not crash.
   update_semantics_callback(&update, (__bridge void*)engine);
 
@@ -632,7 +632,7 @@ - (nonnull NSView*)createWithViewIdentifier:(int64_t)viewId arguments:(nullable
   [threadSynchronizer shutdown];
 
   std::thread rasterThread([&threadSynchronizer] {
-    [threadSynchronizer performCommitForView:kDefaultViewId
+    [threadSynchronizer performCommitForView:kImplicitViewId
                                         size:CGSizeMake(100, 100)
                                       notify:^{
                                       }];
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h b/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h
index 71fe5481cf72b..6b1a4e50e3c5a 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h
+++ b/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h
@@ -115,7 +115,7 @@ typedef NS_ENUM(NSInteger, FlutterAppExitResponse) {
  *
  * Practically, since FlutterEngine can only be attached with one controller,
  * the given controller, if successfully attached, will always have the default
- * view ID kFlutterDefaultViewId.
+ * view ID kFlutterImplicitViewId.
  *
  * The engine holds a weak reference to the attached view controller.
  *
@@ -127,11 +127,11 @@ typedef NS_ENUM(NSInteger, FlutterAppExitResponse) {
 /**
  * Dissociate the given view controller from this engine.
  *
- * Practically, since FlutterEngine can only be attached with one controller,
- * the given controller must be the default view controller.
- *
  * If the view controller is not associated with this engine, this call throws an
  * assertion.
+ *
+ * Practically, since FlutterEngine can only be attached with one controller for
+ * now, the given controller must be the current view controller.
  */
 - (void)removeViewController:(FlutterViewController*)viewController;
 
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterView.h b/shell/platform/darwin/macos/framework/Source/FlutterView.h
index 0c468d4c58d08..6948b880fcf9b 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterView.h
+++ b/shell/platform/darwin/macos/framework/Source/FlutterView.h
@@ -20,7 +20,7 @@ typedef int64_t FlutterViewId;
  * backward compatibility, single-view APIs will always operate on the view with
  * this ID. Also, the first view assigned to the engine will also have this ID.
  */
-constexpr FlutterViewId kFlutterDefaultViewId = 0ll;
+constexpr FlutterViewId kFlutterImplicitViewId = 0ll;
 
 /**
  * Listener for view resizing.
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm b/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm
index 403639b79e62a..aa14b70fc4b2b 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProviderTest.mm
@@ -27,7 +27,7 @@
       .andDo(^(NSInvocation* invocation) {
         FlutterViewId viewId;
         [invocation getArgument:&viewId atIndex:2];
-        if (viewId == kFlutterDefaultViewId) {
+        if (viewId == kFlutterImplicitViewId) {
           if (mockFlutterViewController != nil) {
             [invocation setReturnValue:&mockFlutterViewController];
           }
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm b/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm
index 7599b66e8b0ec..0d6e7cb550400 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterViewTest.mm
@@ -8,7 +8,7 @@
 
 #import "flutter/testing/testing.h"
 
-constexpr int64_t kDefaultViewId = 0ll;
+constexpr int64_t kImplicitViewId = 0ll;
 
 @interface TestReshapeListener : NSObject <FlutterViewReshapeListener>
 
@@ -30,6 +30,6 @@ - (void)viewDidReshape:(nonnull NSView*)view {
                                                 commandQueue:queue
                                              reshapeListener:listener
                                           threadSynchronizer:threadSynchronizer
-                                                      viewId:kDefaultViewId];
+                                                      viewId:kImplicitViewId];
   EXPECT_EQ([view layer:view.layer shouldInheritContentsScale:3.0 fromWindow:view.window], YES);
 }

From d0a43cd774956d291ab321e6957f7962b856bf3c Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 30 Jun 2023 15:29:56 -0700
Subject: [PATCH 02/17] Impl

---
 lib/ui/window/platform_configuration.h        |  9 +++-
 runtime/runtime_controller.cc                 | 19 ++++---
 runtime/runtime_controller.h                  |  2 +-
 shell/common/engine.cc                        |  5 +-
 shell/common/engine.h                         |  2 +-
 shell/common/engine_unittests.cc              |  5 +-
 shell/common/platform_view.cc                 |  5 +-
 shell/common/platform_view.h                  |  3 +-
 shell/common/shell.cc                         |  7 +--
 shell/common/shell.h                          |  1 +
 shell/common/shell_test.cc                    |  6 ++-
 shell/common/shell_unittests.cc               | 54 +++++++++++--------
 .../android/platform_view_android_jni_impl.cc |  5 +-
 .../ios/framework/Source/FlutterEngine.mm     |  4 +-
 .../Source/FlutterEnginePlatformViewTest.mm   |  2 +-
 .../Source/FlutterPlatformViewsTest.mm        |  2 +-
 .../Source/accessibility_bridge_test.mm       |  2 +-
 shell/platform/embedder/embedder.cc           |  6 ++-
 shell/platform/embedder/embedder_engine.cc    |  3 +-
 shell/platform/embedder/embedder_engine.h     |  3 +-
 .../platform_view_embedder_unittests.cc       |  4 +-
 .../fuchsia/flutter/flatland_platform_view.cc | 51 +++++++++---------
 .../fuchsia/flutter/gfx_platform_view.cc      | 48 +++++++++--------
 .../fuchsia/flutter/platform_view_unittest.cc |  1 +
 .../tests/flatland_platform_view_unittest.cc  |  1 +
 shell/testing/tester_main.cc                  |  4 +-
 26 files changed, 156 insertions(+), 98 deletions(-)

diff --git a/lib/ui/window/platform_configuration.h b/lib/ui/window/platform_configuration.h
index c03f38194bf50..77836717809e8 100644
--- a/lib/ui/window/platform_configuration.h
+++ b/lib/ui/window/platform_configuration.h
@@ -415,7 +415,14 @@ class PlatformConfiguration final {
   ///
   /// @return     a pointer to the Window.
   ///
-  Window* get_window(int window_id) { return windows_[window_id].get(); }
+  Window* get_window(int window_id) {
+    auto found = windows_.find(window_id);
+    if (found != windows_.end()) {
+      return found->second.get();
+    } else {
+      return nullptr;
+    }
+  }
 
   //----------------------------------------------------------------------------
   /// @brief      Responds to a previous platform message to the engine from the
diff --git a/runtime/runtime_controller.cc b/runtime/runtime_controller.cc
index 5ffd02d099139..9cc704a8e7077 100644
--- a/runtime/runtime_controller.cc
+++ b/runtime/runtime_controller.cc
@@ -20,7 +20,7 @@
 
 namespace flutter {
 
-const uint64_t kFlutterDefaultViewId = 0llu;
+constexpr uint64_t kFlutterImplicitViewId = 0ll;
 
 RuntimeController::RuntimeController(RuntimeDelegate& p_client,
                                      const TaskRunners& task_runners)
@@ -115,7 +115,10 @@ std::unique_ptr<RuntimeController> RuntimeController::Clone() const {
 }
 
 bool RuntimeController::FlushRuntimeStateToIsolate() {
-  return SetViewportMetrics(platform_data_.viewport_metrics) &&
+  // TODO(dkwingsmt): Needs a view ID here (or platform_data should probably
+  // have multiple view metrics).
+  return SetViewportMetrics(kFlutterImplicitViewId,
+                            platform_data_.viewport_metrics) &&
          SetLocales(platform_data_.locale_data) &&
          SetSemanticsEnabled(platform_data_.semantics_enabled) &&
          SetAccessibilityFeatures(
@@ -125,13 +128,17 @@ bool RuntimeController::FlushRuntimeStateToIsolate() {
          SetDisplays(platform_data_.displays);
 }
 
-bool RuntimeController::SetViewportMetrics(const ViewportMetrics& metrics) {
+bool RuntimeController::SetViewportMetrics(int64_t view_id,
+                                           const ViewportMetrics& metrics) {
   TRACE_EVENT0("flutter", "SetViewportMetrics");
   platform_data_.viewport_metrics = metrics;
 
   if (auto* platform_configuration = GetPlatformConfigurationIfAvailable()) {
-    platform_configuration->get_window(0)->UpdateWindowMetrics(metrics);
-    return true;
+    Window* window = platform_configuration->get_window(view_id);
+    if (window) {
+      window->UpdateWindowMetrics(metrics);
+      return true;
+    }
   }
 
   return false;
@@ -320,7 +327,7 @@ void RuntimeController::ScheduleFrame() {
 // |PlatformConfigurationClient|
 void RuntimeController::Render(Scene* scene) {
   // TODO(dkwingsmt): Currently only supports a single window.
-  int64_t view_id = kFlutterDefaultViewId;
+  int64_t view_id = kFlutterImplicitViewId;
   auto window =
       UIDartState::Current()->platform_configuration()->get_window(view_id);
   if (window == nullptr) {
diff --git a/runtime/runtime_controller.h b/runtime/runtime_controller.h
index 1df085262f605..b4b1fcc8d3c8d 100644
--- a/runtime/runtime_controller.h
+++ b/runtime/runtime_controller.h
@@ -172,7 +172,7 @@ class RuntimeController : public PlatformConfigurationClient {
   ///
   /// @return     If the window metrics were forwarded to the running isolate.
   ///
-  bool SetViewportMetrics(const ViewportMetrics& metrics);
+  bool SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Forward the specified display metrics to the running isolate.
diff --git a/shell/common/engine.cc b/shell/common/engine.cc
index 2c0b22d1863f8..33d8e52baf40d 100644
--- a/shell/common/engine.cc
+++ b/shell/common/engine.cc
@@ -292,8 +292,9 @@ tonic::DartErrorHandleType Engine::GetUIIsolateLastError() {
   return runtime_controller_->GetLastError();
 }
 
-void Engine::SetViewportMetrics(const ViewportMetrics& metrics) {
-  runtime_controller_->SetViewportMetrics(metrics);
+void Engine::SetViewportMetrics(int64_t view_id,
+                                const ViewportMetrics& metrics) {
+  runtime_controller_->SetViewportMetrics(view_id, metrics);
   ScheduleFrame();
 }
 
diff --git a/shell/common/engine.h b/shell/common/engine.h
index 1890589729b04..d141ffa0cc28a 100644
--- a/shell/common/engine.h
+++ b/shell/common/engine.h
@@ -686,7 +686,7 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   ///
   /// @param[in]  metrics  The metrics
   ///
-  void SetViewportMetrics(const ViewportMetrics& metrics);
+  void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Updates the display metrics for the currently running Flutter
diff --git a/shell/common/engine_unittests.cc b/shell/common/engine_unittests.cc
index 5011f266557c8..995c408247ef4 100644
--- a/shell/common/engine_unittests.cc
+++ b/shell/common/engine_unittests.cc
@@ -21,6 +21,8 @@
 namespace flutter {
 
 namespace {
+constexpr int64_t kDefaultViewId = 0ll;
+
 class MockDelegate : public Engine::Delegate {
  public:
   MOCK_METHOD2(OnEngineUpdateSemantics,
@@ -330,7 +332,8 @@ TEST_F(EngineTest, SpawnResetsViewportMetrics) {
     const double kViewHeight = 1024;
     old_viewport_metrics.physical_width = kViewWidth;
     old_viewport_metrics.physical_height = kViewHeight;
-    mock_runtime_controller->SetViewportMetrics(old_viewport_metrics);
+    mock_runtime_controller->SetViewportMetrics(kDefaultViewId,
+                                                old_viewport_metrics);
     auto engine = std::make_unique<Engine>(
         /*delegate=*/delegate_,
         /*dispatcher_maker=*/dispatcher_maker_,
diff --git a/shell/common/platform_view.cc b/shell/common/platform_view.cc
index 7cb0b091d5bcd..77a33bfb76e2a 100644
--- a/shell/common/platform_view.cc
+++ b/shell/common/platform_view.cc
@@ -51,8 +51,9 @@ void PlatformView::SetAccessibilityFeatures(int32_t flags) {
   delegate_.OnPlatformViewSetAccessibilityFeatures(flags);
 }
 
-void PlatformView::SetViewportMetrics(const ViewportMetrics& metrics) {
-  delegate_.OnPlatformViewSetViewportMetrics(metrics);
+void PlatformView::SetViewportMetrics(int64_t view_id,
+                                      const ViewportMetrics& metrics) {
+  delegate_.OnPlatformViewSetViewportMetrics(view_id, metrics);
 }
 
 void PlatformView::NotifyCreated() {
diff --git a/shell/common/platform_view.h b/shell/common/platform_view.h
index 9ec848e34568d..3e5aab515ccd8 100644
--- a/shell/common/platform_view.h
+++ b/shell/common/platform_view.h
@@ -112,6 +112,7 @@ class PlatformView {
     /// @param[in]  metrics  The updated viewport metrics.
     ///
     virtual void OnPlatformViewSetViewportMetrics(
+        int64_t view_id,
         const ViewportMetrics& metrics) = 0;
 
     //--------------------------------------------------------------------------
@@ -474,7 +475,7 @@ class PlatformView {
   ///
   /// @param[in]  metrics  The updated viewport metrics.
   ///
-  void SetViewportMetrics(const ViewportMetrics& metrics);
+  void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Used by embedders to notify the shell that a platform view
diff --git a/shell/common/shell.cc b/shell/common/shell.cc
index 859a2668c3762..23de5bea8f0fd 100644
--- a/shell/common/shell.cc
+++ b/shell/common/shell.cc
@@ -954,7 +954,8 @@ void Shell::OnPlatformViewScheduleFrame() {
 }
 
 // |PlatformView::Delegate|
-void Shell::OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) {
+void Shell::OnPlatformViewSetViewportMetrics(int64_t view_id,
+                                             const ViewportMetrics& metrics) {
   FML_DCHECK(is_setup_);
   FML_DCHECK(task_runners_.GetPlatformTaskRunner()->RunsTasksOnCurrentThread());
 
@@ -978,9 +979,9 @@ void Shell::OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) {
       });
 
   task_runners_.GetUITaskRunner()->PostTask(
-      [engine = engine_->GetWeakPtr(), metrics]() {
+      [engine = engine_->GetWeakPtr(), metrics, view_id]() {
         if (engine) {
-          engine->SetViewportMetrics(metrics);
+          engine->SetViewportMetrics(view_id, metrics);
         }
       });
 
diff --git a/shell/common/shell.h b/shell/common/shell.h
index d913c3e9c84a6..6c104f8558f4a 100644
--- a/shell/common/shell.h
+++ b/shell/common/shell.h
@@ -544,6 +544,7 @@ class Shell final : public PlatformView::Delegate,
 
   // |PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const ViewportMetrics& metrics) override;
 
   // |PlatformView::Delegate|
diff --git a/shell/common/shell_test.cc b/shell/common/shell_test.cc
index 5e5d38d2b2b94..b892faefcef84 100644
--- a/shell/common/shell_test.cc
+++ b/shell/common/shell_test.cc
@@ -20,6 +20,8 @@
 namespace flutter {
 namespace testing {
 
+constexpr int64_t kDefaultViewId = 0;
+
 ShellTest::ShellTest()
     : thread_host_("io.flutter.test." + GetCurrentTestName() + ".",
                    ThreadHost::Type::Platform | ThreadHost::Type::IO |
@@ -144,7 +146,7 @@ void ShellTest::SetViewportMetrics(Shell* shell, double width, double height) {
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
         if (engine) {
-          engine->SetViewportMetrics(viewport_metrics);
+          engine->SetViewportMetrics(kDefaultViewId, viewport_metrics);
           const auto frame_begin_time = fml::TimePoint::Now();
           const auto frame_end_time =
               frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);
@@ -186,7 +188,7 @@ void ShellTest::PumpOneFrame(Shell* shell,
   fml::AutoResetWaitableEvent latch;
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
-        engine->SetViewportMetrics(viewport_metrics);
+        engine->SetViewportMetrics(kDefaultViewId, viewport_metrics);
         const auto frame_begin_time = fml::TimePoint::Now();
         const auto frame_end_time =
             frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);
diff --git a/shell/common/shell_unittests.cc b/shell/common/shell_unittests.cc
index 16abef0dbc0f3..e9c606b704743 100644
--- a/shell/common/shell_unittests.cc
+++ b/shell/common/shell_unittests.cc
@@ -60,6 +60,8 @@
 namespace flutter {
 namespace testing {
 
+constexpr int64_t kDefaultViewId = 0ll;
+
 using ::testing::_;
 using ::testing::Return;
 
@@ -74,8 +76,8 @@ class MockPlatformViewDelegate : public PlatformView::Delegate {
   MOCK_METHOD1(OnPlatformViewSetNextFrameCallback,
                void(const fml::closure& closure));
 
-  MOCK_METHOD1(OnPlatformViewSetViewportMetrics,
-               void(const ViewportMetrics& metrics));
+  MOCK_METHOD2(OnPlatformViewSetViewportMetrics,
+               void(int64_t view_id, const ViewportMetrics& metrics));
 
   MOCK_METHOD1(OnPlatformViewDispatchPlatformMessage,
                void(std::unique_ptr<PlatformMessage> message));
@@ -1637,7 +1639,8 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
 
   RunEngine(shell.get(), std::move(configuration));
   PostSync(shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-    shell->GetPlatformView()->SetViewportMetrics({1.0, 100, 100, 22, 0});
+    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                 {1.0, 100, 100, 22, 0});
   });
 
   // first cache bytes
@@ -1666,7 +1669,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 100, 22, 0});
+                 kDefaultViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1675,7 +1678,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 300, 22, 0});
+                 kDefaultViewId, {1.0, 100, 300, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1686,7 +1689,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 400, 100, 22, 0});
+                 kDefaultViewId, {1.0, 400, 100, 22, 0});
            });
   // first cache bytes + second cache bytes + third cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1695,7 +1698,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 800, 100, 22, 0});
+                 kDefaultViewId, {1.0, 800, 100, 22, 0});
            });
   // max bytes threshold
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1708,7 +1711,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 100, 22, 0});
+                 kDefaultViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1752,7 +1755,8 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1772,7 +1776,8 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 800, 400, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                     {1.0, 800, 400, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1789,7 +1794,8 @@ TEST_F(ShellTest, SetResourceCacheSizeEarly) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1816,7 +1822,8 @@ TEST_F(ShellTest, SetResourceCacheSizeNotifiesDart) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -2683,6 +2690,7 @@ TEST_F(ShellTest, DISABLED_DiscardLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &expected_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
+            kDefaultViewId,
             {1.0, static_cast<double>(expected_size.width()),
              static_cast<double>(expected_size.height()), 22, 0});
       });
@@ -2760,8 +2768,8 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &origin_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            {1.0, static_cast<double>(origin_size.width()),
-             static_cast<double>(origin_size.height()), 22, 0});
+            kDefaultViewId, {1.0, static_cast<double>(origin_size.width()),
+                             static_cast<double>(origin_size.height()), 22, 0});
       });
 
   auto configuration = RunConfiguration::InferFromSettings(settings);
@@ -2779,8 +2787,8 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &new_size, &resize_latch]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            {1.0, static_cast<double>(new_size.width()),
-             static_cast<double>(new_size.height()), 22, 0});
+            kDefaultViewId, {1.0, static_cast<double>(new_size.width()),
+                             static_cast<double>(new_size.height()), 22, 0});
         resize_latch.Signal();
       });
 
@@ -2843,14 +2851,17 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   RunEngine(shell.get(), std::move(configuration));
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics({0.0, 400, 200, 22, 0});
+    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                 {0.0, 400, 200, 22, 0});
     task_runner->PostTask([&]() {
-      shell->GetPlatformView()->SetViewportMetrics({0.8, 0.0, 200, 22, 0});
+      shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                   {0.8, 0.0, 200, 22, 0});
       task_runner->PostTask([&]() {
-        shell->GetPlatformView()->SetViewportMetrics({0.8, 400, 0.0, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                     {0.8, 400, 0.0, 22, 0});
         task_runner->PostTask([&]() {
           shell->GetPlatformView()->SetViewportMetrics(
-              {0.8, 400, 200.0, 22, 0});
+              kDefaultViewId, {0.8, 400, 200.0, 22, 0});
         });
       });
     });
@@ -2862,7 +2873,8 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   latch.Reset();
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics({1.2, 600, 300, 22, 0});
+    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+                                                 {1.2, 600, 300, 22, 0});
   });
   latch.Wait();
   ASSERT_EQ(last_device_pixel_ratio, 1.2);
diff --git a/shell/platform/android/platform_view_android_jni_impl.cc b/shell/platform/android/platform_view_android_jni_impl.cc
index c4580bc0562d7..72abd446061b0 100644
--- a/shell/platform/android/platform_view_android_jni_impl.cc
+++ b/shell/platform/android/platform_view_android_jni_impl.cc
@@ -37,6 +37,8 @@
 
 namespace flutter {
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 static fml::jni::ScopedJavaGlobalRef<jclass>* g_flutter_callback_info_class =
     nullptr;
 
@@ -338,7 +340,8 @@ static void SetViewportMetrics(JNIEnv* env,
       0,  // Display ID
   };
 
-  ANDROID_SHELL_HOLDER->GetPlatformView()->SetViewportMetrics(metrics);
+  ANDROID_SHELL_HOLDER->GetPlatformView()->SetViewportMetrics(
+      kFlutterImplicitViewId, metrics);
 }
 
 static void UpdateDisplayMetrics(JNIEnv* env,
diff --git a/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm b/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm
index 52e6af116b079..1130dcccf7efe 100644
--- a/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm
+++ b/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm
@@ -38,6 +38,8 @@
 #import "flutter/shell/platform/darwin/ios/rendering_api_selection.h"
 #include "flutter/shell/profiling/sampling_profiler.h"
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 /// Inheriting ThreadConfigurer and use iOS platform thread API to configure the thread priorities
 /// Using iOS platform thread API to configure thread priority
 static void IOSPlatformThreadConfigSetter(const fml::Thread::ThreadConfig& config) {
@@ -308,7 +310,7 @@ - (void)updateViewportMetrics:(flutter::ViewportMetrics)viewportMetrics {
   if (!self.platformView) {
     return;
   }
-  self.platformView->SetViewportMetrics(viewportMetrics);
+  self.platformView->SetViewportMetrics(kFlutterImplicitViewId, viewportMetrics);
 }
 
 - (void)dispatchPointerDataPacket:(std::unique_ptr<flutter::PointerDataPacket>)packet {
diff --git a/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm b/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm
index e4341a065c2af..0b5526a5341a2 100644
--- a/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm
+++ b/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm
@@ -24,7 +24,7 @@ void OnPlatformViewCreated(std::unique_ptr<Surface> surface) override {}
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {
diff --git a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm
index 974eb31de9f44..bba450217747a 100644
--- a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm
+++ b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm
@@ -93,7 +93,7 @@ void OnPlatformViewCreated(std::unique_ptr<Surface> surface) override {}
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {
diff --git a/shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm b/shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm
index 40995c9111284..283d4fe02decd 100644
--- a/shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm
+++ b/shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm
@@ -77,7 +77,7 @@ void OnPlatformViewCreated(std::unique_ptr<Surface> surface) override {}
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {
diff --git a/shell/platform/embedder/embedder.cc b/shell/platform/embedder/embedder.cc
index c9d1ce9866744..008ea576482d5 100644
--- a/shell/platform/embedder/embedder.cc
+++ b/shell/platform/embedder/embedder.cc
@@ -83,6 +83,8 @@ extern const intptr_t kPlatformStrongDillSize;
 const int32_t kFlutterSemanticsNodeIdBatchEnd = -1;
 const int32_t kFlutterSemanticsCustomActionIdBatchEnd = -1;
 
+static constexpr int64_t kFlutterImplicitViewId = 0;
+
 // A message channel to send platform-independent FlutterKeyData to the
 // framework.
 //
@@ -2186,6 +2188,8 @@ FlutterEngineResult FlutterEngineSendWindowMetricsEvent(
   if (engine == nullptr || flutter_metrics == nullptr) {
     return LOG_EMBEDDER_ERROR(kInvalidArguments, "Engine handle was invalid.");
   }
+  // TODO(dkwingsmt): Use a real view ID when multiview is supported.
+  int64_t view_id = kFlutterImplicitViewId;
 
   flutter::ViewportMetrics metrics;
 
@@ -2227,7 +2231,7 @@ FlutterEngineResult FlutterEngineSendWindowMetricsEvent(
   }
 
   return reinterpret_cast<flutter::EmbedderEngine*>(engine)->SetViewportMetrics(
-             metrics)
+             view_id, metrics)
              ? kSuccess
              : LOG_EMBEDDER_ERROR(kInvalidArguments,
                                   "Viewport metrics were invalid.");
diff --git a/shell/platform/embedder/embedder_engine.cc b/shell/platform/embedder/embedder_engine.cc
index cc4da738f72fc..b34da8a287f4e 100644
--- a/shell/platform/embedder/embedder_engine.cc
+++ b/shell/platform/embedder/embedder_engine.cc
@@ -100,6 +100,7 @@ bool EmbedderEngine::NotifyDestroyed() {
 }
 
 bool EmbedderEngine::SetViewportMetrics(
+    int64_t view_id,
     const flutter::ViewportMetrics& metrics) {
   if (!IsValid()) {
     return false;
@@ -109,7 +110,7 @@ bool EmbedderEngine::SetViewportMetrics(
   if (!platform_view) {
     return false;
   }
-  platform_view->SetViewportMetrics(metrics);
+  platform_view->SetViewportMetrics(view_id, metrics);
   return true;
 }
 
diff --git a/shell/platform/embedder/embedder_engine.h b/shell/platform/embedder/embedder_engine.h
index 60d33ba76e652..a587eeb3eaa74 100644
--- a/shell/platform/embedder/embedder_engine.h
+++ b/shell/platform/embedder/embedder_engine.h
@@ -48,7 +48,8 @@ class EmbedderEngine {
 
   bool IsValid() const;
 
-  bool SetViewportMetrics(const flutter::ViewportMetrics& metrics);
+  bool SetViewportMetrics(int64_t view_id,
+                          const flutter::ViewportMetrics& metrics);
 
   bool DispatchPointerDataPacket(
       std::unique_ptr<flutter::PointerDataPacket> packet);
diff --git a/shell/platform/embedder/platform_view_embedder_unittests.cc b/shell/platform/embedder/platform_view_embedder_unittests.cc
index 3e795f1fb530f..d22dc030e7292 100644
--- a/shell/platform/embedder/platform_view_embedder_unittests.cc
+++ b/shell/platform/embedder/platform_view_embedder_unittests.cc
@@ -21,8 +21,8 @@ class MockDelegate : public PlatformView::Delegate {
   MOCK_METHOD0(OnPlatformViewScheduleFrame, void());
   MOCK_METHOD1(OnPlatformViewSetNextFrameCallback,
                void(const fml::closure& closure));
-  MOCK_METHOD1(OnPlatformViewSetViewportMetrics,
-               void(const ViewportMetrics& metrics));
+  MOCK_METHOD2(OnPlatformViewSetViewportMetrics,
+               void(int64_t view_id, const ViewportMetrics& metrics));
   MOCK_METHOD1(OnPlatformViewDispatchPlatformMessage,
                void(std::unique_ptr<PlatformMessage> message));
   MOCK_METHOD1(OnPlatformViewDispatchPointerDataPacket,
diff --git a/shell/platform/fuchsia/flutter/flatland_platform_view.cc b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
index cbadf9d47b6e0..e9c55f87f539e 100644
--- a/shell/platform/fuchsia/flutter/flatland_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
@@ -8,6 +8,8 @@
 
 namespace flutter_runner {
 
+static constexpr int64_t kFlutterDefaultViewId = 0ll;
+
 FlatlandPlatformView::FlatlandPlatformView(
     flutter::PlatformView::Delegate& delegate,
     flutter::TaskRunners task_runners,
@@ -85,30 +87,31 @@ void FlatlandPlatformView::OnGetLayout(
 
   float pixel_ratio = view_pixel_ratio_ ? *view_pixel_ratio_ : 1.0f;
 
-  SetViewportMetrics({
-      pixel_ratio,  // device_pixel_ratio
-      std::round(view_logical_size_.value()[0] *
-                 pixel_ratio),  // physical_width
-      std::round(view_logical_size_.value()[1] *
-                 pixel_ratio),  // physical_height
-      0.0f,                     // physical_padding_top
-      0.0f,                     // physical_padding_right
-      0.0f,                     // physical_padding_bottom
-      0.0f,                     // physical_padding_left
-      0.0f,                     // physical_view_inset_top
-      0.0f,                     // physical_view_inset_right
-      0.0f,                     // physical_view_inset_bottom
-      0.0f,                     // physical_view_inset_left
-      0.0f,                     // p_physical_system_gesture_inset_top
-      0.0f,                     // p_physical_system_gesture_inset_right
-      0.0f,                     // p_physical_system_gesture_inset_bottom
-      0.0f,                     // p_physical_system_gesture_inset_left,
-      -1.0,                     // p_physical_touch_slop,
-      {},                       // p_physical_display_features_bounds
-      {},                       // p_physical_display_features_type
-      {},                       // p_physical_display_features_state
-      0,                        // p_display_id
-  });
+  SetViewportMetrics(kFlutterDefaultViewId,
+                     {
+                         pixel_ratio,  // device_pixel_ratio
+                         std::round(view_logical_size_.value()[0] *
+                                    pixel_ratio),  // physical_width
+                         std::round(view_logical_size_.value()[1] *
+                                    pixel_ratio),  // physical_height
+                         0.0f,                     // physical_padding_top
+                         0.0f,                     // physical_padding_right
+                         0.0f,                     // physical_padding_bottom
+                         0.0f,                     // physical_padding_left
+                         0.0f,                     // physical_view_inset_top
+                         0.0f,                     // physical_view_inset_right
+                         0.0f,                     // physical_view_inset_bottom
+                         0.0f,                     // physical_view_inset_left
+                         0.0f,  // p_physical_system_gesture_inset_top
+                         0.0f,  // p_physical_system_gesture_inset_right
+                         0.0f,  // p_physical_system_gesture_inset_bottom
+                         0.0f,  // p_physical_system_gesture_inset_left,
+                         -1.0,  // p_physical_touch_slop,
+                         {},    // p_physical_display_features_bounds
+                         {},    // p_physical_display_features_type
+                         {},    // p_physical_display_features_state
+                         0,     // p_display_id
+                     });
 
   parent_viewport_watcher_->GetLayout(
       fit::bind_member(this, &FlatlandPlatformView::OnGetLayout));
diff --git a/shell/platform/fuchsia/flutter/gfx_platform_view.cc b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
index df0e9906caf50..149e91d7135af 100644
--- a/shell/platform/fuchsia/flutter/gfx_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
@@ -8,6 +8,8 @@
 
 namespace flutter_runner {
 
+static constexpr int64_t kFlutterDefaultViewId = 0ll;
+
 GfxPlatformView::GfxPlatformView(
     flutter::PlatformView::Delegate& delegate,
     flutter::TaskRunners task_runners,
@@ -213,28 +215,30 @@ void GfxPlatformView::OnScenicEvent(
       metrics_changed) {
     const float pixel_ratio = *view_pixel_ratio_;
     const std::array<float, 2> logical_size = *view_logical_size_;
-    SetViewportMetrics({
-        pixel_ratio,                                // device_pixel_ratio
-        std::round(logical_size[0] * pixel_ratio),  // physical_width
-        std::round(logical_size[1] * pixel_ratio),  // physical_height
-        0.0f,                                       // physical_padding_top
-        0.0f,                                       // physical_padding_right
-        0.0f,                                       // physical_padding_bottom
-        0.0f,                                       // physical_padding_left
-        0.0f,                                       // physical_view_inset_top
-        0.0f,                                       // physical_view_inset_right
-        0.0f,  // physical_view_inset_bottom
-        0.0f,  // physical_view_inset_left
-        0.0f,  // p_physical_system_gesture_inset_top
-        0.0f,  // p_physical_system_gesture_inset_right
-        0.0f,  // p_physical_system_gesture_inset_bottom
-        0.0f,  // p_physical_system_gesture_inset_left,
-        -1.0,  // p_physical_touch_slop,
-        {},    // p_physical_display_features_bounds
-        {},    // p_physical_display_features_type
-        {},    // p_physical_display_features_state
-        0,     // pdisplay_id
-    });
+    SetViewportMetrics(
+        kFlutterDefaultViewId,
+        {
+            pixel_ratio,                                // device_pixel_ratio
+            std::round(logical_size[0] * pixel_ratio),  // physical_width
+            std::round(logical_size[1] * pixel_ratio),  // physical_height
+            0.0f,                                       // physical_padding_top
+            0.0f,  // physical_padding_right
+            0.0f,  // physical_padding_bottom
+            0.0f,  // physical_padding_left
+            0.0f,  // physical_view_inset_top
+            0.0f,  // physical_view_inset_right
+            0.0f,  // physical_view_inset_bottom
+            0.0f,  // physical_view_inset_left
+            0.0f,  // p_physical_system_gesture_inset_top
+            0.0f,  // p_physical_system_gesture_inset_right
+            0.0f,  // p_physical_system_gesture_inset_bottom
+            0.0f,  // p_physical_system_gesture_inset_left,
+            -1.0,  // p_physical_touch_slop,
+            {},    // p_physical_display_features_bounds
+            {},    // p_physical_display_features_type
+            {},    // p_physical_display_features_state
+            0,     // pdisplay_id
+        });
   }
 }
 
diff --git a/shell/platform/fuchsia/flutter/platform_view_unittest.cc b/shell/platform/fuchsia/flutter/platform_view_unittest.cc
index c0aa42e0a5dbf..54a9c7a593f3b 100644
--- a/shell/platform/fuchsia/flutter/platform_view_unittest.cc
+++ b/shell/platform/fuchsia/flutter/platform_view_unittest.cc
@@ -90,6 +90,7 @@ class MockPlatformViewDelegate : public flutter::PlatformView::Delegate {
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) {}
   // |flutter::PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const flutter::ViewportMetrics& metrics) {
     metrics_ = metrics;
   }
diff --git a/shell/platform/fuchsia/flutter/tests/flatland_platform_view_unittest.cc b/shell/platform/fuchsia/flutter/tests/flatland_platform_view_unittest.cc
index 78f6f9588958a..ff4347015eb49 100644
--- a/shell/platform/fuchsia/flutter/tests/flatland_platform_view_unittest.cc
+++ b/shell/platform/fuchsia/flutter/tests/flatland_platform_view_unittest.cc
@@ -89,6 +89,7 @@ class MockPlatformViewDelegate : public flutter::PlatformView::Delegate {
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) {}
   // |flutter::PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const flutter::ViewportMetrics& metrics) {
     metrics_ = metrics;
   }
diff --git a/shell/testing/tester_main.cc b/shell/testing/tester_main.cc
index 342b4ea7aebe9..a6719ede8ffdf 100644
--- a/shell/testing/tester_main.cc
+++ b/shell/testing/tester_main.cc
@@ -39,6 +39,8 @@
 
 namespace flutter {
 
+static constexpr int64_t kDefaultViewId = 0ll;
+
 class TesterExternalViewEmbedder : public ExternalViewEmbedder {
   // |ExternalViewEmbedder|
   DlCanvas* GetRootCanvas() override { return nullptr; }
@@ -353,7 +355,7 @@ int RunTester(const flutter::Settings& settings,
   metrics.physical_width = physical_width;
   metrics.physical_height = physical_height;
   metrics.display_id = 0;
-  shell->GetPlatformView()->SetViewportMetrics(metrics);
+  shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId, metrics);
 
   // Run the message loop and wait for the script to do its thing.
   fml::MessageLoop::GetCurrent().Run();

From 3d86303df29bf2f69cc543c1ab5e03d4aae54649 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Wed, 5 Jul 2023 08:45:15 -0700
Subject: [PATCH 03/17] Fix doc

---
 .../framework/Headers/FlutterPluginRegistrarMacOS.h      | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index 0a5ae5dd695a8..ef4868469f951 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -38,7 +38,14 @@ FLUTTER_DARWIN_EXPORT
 /**
  * The view displaying Flutter content.
  *
- * This method may return |nil|, for instance in a headless environment.
+ * Some single-view APIs will eventually be replaced by their multi-view
+ * variant. During the deprecation period, the single-view APIs will coexist
+ * with and work with the multi-view APIs as if the other views don't exist.
+ * For backward compatibility, single-view APIs will always operate on this
+ * view, which is the first view assigned to the engine.
+ *
+ * This method may return |nil|, for instance in a headless environment, or when
+ * multi-view is supported in the future and the compatible mode is disabled.
  */
 @property(nullable, readonly) NSView* view;
 

From 1a69ee9fcb742e7032931e7f909757b1315b47f8 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Wed, 5 Jul 2023 10:36:52 -0700
Subject: [PATCH 04/17] Move get_window to cc

---
 lib/ui/window/platform_configuration.cc |  9 +++++++++
 lib/ui/window/platform_configuration.h  | 14 ++++----------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/lib/ui/window/platform_configuration.cc b/lib/ui/window/platform_configuration.cc
index b1cd11fad30e7..fe6ff03d62b69 100644
--- a/lib/ui/window/platform_configuration.cc
+++ b/lib/ui/window/platform_configuration.cc
@@ -308,6 +308,15 @@ void PlatformConfiguration::ReportTimings(std::vector<int64_t> timings) {
                                                }));
 }
 
+Window* PlatformConfiguration::get_window(int window_id) {
+  auto found = windows_.find(window_id);
+  if (found != windows_.end()) {
+    return found->second.get();
+  } else {
+    return nullptr;
+  }
+}
+
 void PlatformConfiguration::CompletePlatformMessageEmptyResponse(
     int response_id) {
   if (!response_id) {
diff --git a/lib/ui/window/platform_configuration.h b/lib/ui/window/platform_configuration.h
index 77836717809e8..9226b457d07e8 100644
--- a/lib/ui/window/platform_configuration.h
+++ b/lib/ui/window/platform_configuration.h
@@ -413,16 +413,10 @@ class PlatformConfiguration final {
   ///
   /// @param[in] window_id The id of the window to find and return.
   ///
-  /// @return     a pointer to the Window.
-  ///
-  Window* get_window(int window_id) {
-    auto found = windows_.find(window_id);
-    if (found != windows_.end()) {
-      return found->second.get();
-    } else {
-      return nullptr;
-    }
-  }
+  /// @return     a pointer to the Window. Returns nullptr if the ID is not
+  ///             found.
+  ///
+  Window* get_window(int window_id);
 
   //----------------------------------------------------------------------------
   /// @brief      Responds to a previous platform message to the engine from the

From a293b8e35da0de772eaf0810ed3b03ba09d6fcc9 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Wed, 5 Jul 2023 22:18:48 -0700
Subject: [PATCH 05/17] Fix doc

---
 .../Headers/FlutterPluginRegistrarMacOS.h          | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index ef4868469f951..dea07ed530929 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -38,11 +38,15 @@ FLUTTER_DARWIN_EXPORT
 /**
  * The view displaying Flutter content.
  *
- * Some single-view APIs will eventually be replaced by their multi-view
- * variant. During the deprecation period, the single-view APIs will coexist
- * with and work with the multi-view APIs as if the other views don't exist.
- * For backward compatibility, single-view APIs will always operate on this
- * view, which is the first view assigned to the engine.
+ * Currently Flutter only supports one view, and this is the view. Flutter
+ * plans to support multiple views in the future. Although single-view APIs
+ * will eventually be replaced by their multi-view variant, there will be
+ * a deprecation period, during the single-view APIs coexist with and work with
+ * the multi-view APIs as if the other views don't exist. This
+ * field therefore guarantees backward-compatible behavior in that:
+ *
+ *  - The first view attached to the engine becomes the value of this field.
+ *  - Single-view Flutter APIs operate the value of this field.
  *
  * This method may return |nil|, for instance in a headless environment, or when
  * multi-view is supported in the future and the compatible mode is disabled.

From 7699ee816aec141407108995cfa75b6f07d75e96 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Wed, 5 Jul 2023 22:38:25 -0700
Subject: [PATCH 06/17] Better doc

---
 .../Headers/FlutterPluginRegistrarMacOS.h     | 30 ++++++++++++-------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index dea07ed530929..d129f870ecb11 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -38,18 +38,28 @@ FLUTTER_DARWIN_EXPORT
 /**
  * The view displaying Flutter content.
  *
- * Currently Flutter only supports one view, and this is the view. Flutter
- * plans to support multiple views in the future. Although single-view APIs
- * will eventually be replaced by their multi-view variant, there will be
- * a deprecation period, during the single-view APIs coexist with and work with
- * the multi-view APIs as if the other views don't exist. This
- * field therefore guarantees backward-compatible behavior in that:
+ * Currently Flutter only supports one view, and this is the view.
  *
- *  - The first view attached to the engine becomes the value of this field.
- *  - Single-view Flutter APIs operate the value of this field.
+ * Flutter plans to support multiple views in the future. Although single-view
+ * APIs will eventually be replaced by their multi-view variants, during the
+ * deprecation period, the single-view APIs will coexist with and work with the
+ * multi-view APIs as if the other views don't exist. To achieve this,
+ * all behaviors of "the single view" (which is called "the implicit view") are
+ * preserved, allowing legacy single-view APIs to continue working, while
+ * new-style views created by new ways must be operated by the upcoming
+ * multi-view APIs.
  *
- * This method may return |nil|, for instance in a headless environment, or when
- * multi-view is supported in the future and the compatible mode is disabled.
+ * Plugins written for a single view can keep operating on this view and expect
+ * unchanged behavior for the implicit view. This includes that:
+ *
+ *  - The first view controller attached to the engine will be linked to the
+ *    implicit view.
+ *  - Single-view Flutter APIs will operate the implicit view.
+ *
+ * This method may return |nil| if the view is not assigned. In single-view
+ * apps, this means that the app is running headlessly. In multi-view apps,
+ * this means that the compatible mode is disabled, or that the compatible mode
+ * is on but no view controller has been attached to the engine yet.
  */
 @property(nullable, readonly) NSView* view;
 

From 85adee8f9102321d5c4dbc4862a03102661656c9 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Thu, 6 Jul 2023 09:54:01 -0700
Subject: [PATCH 07/17] Add view update test

---
 .../platform_configuration_unittests.cc       | 66 +++++++++++++++++--
 1 file changed, 60 insertions(+), 6 deletions(-)

diff --git a/lib/ui/window/platform_configuration_unittests.cc b/lib/ui/window/platform_configuration_unittests.cc
index e89a5cc7d381c..a9146790c2dc2 100644
--- a/lib/ui/window/platform_configuration_unittests.cc
+++ b/lib/ui/window/platform_configuration_unittests.cc
@@ -19,7 +19,7 @@
 namespace flutter {
 namespace testing {
 
-TEST_F(ShellTest, PlatformConfigurationInitialization) {
+TEST_F(PlatformConfigurationTest, Initialization) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
   auto nativeValidateConfiguration = [message_latch](
@@ -63,7 +63,7 @@ TEST_F(ShellTest, PlatformConfigurationInitialization) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationWindowMetricsUpdate) {
+TEST_F(PlatformConfigurationTest, WindowMetricsUpdate) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
   auto nativeValidateConfiguration = [message_latch](
@@ -113,7 +113,61 @@ TEST_F(ShellTest, PlatformConfigurationWindowMetricsUpdate) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorHandlesError) {
+TEST_F(PlatformConfigurationTest,
+       RegularWindowIsUnavailableUntilMetricsUpdate) {
+  auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
+
+  auto nativeValidateConfiguration = [message_latch](
+                                         Dart_NativeArguments args) {
+    PlatformConfiguration* configuration =
+        UIDartState::Current()->platform_configuration();
+
+    // Non-implicit views should not be created at startup
+    ASSERT_EQ(configuration->get_window(1), nullptr);
+    configuration->get_window(1)->UpdateWindowMetrics(
+        ViewportMetrics{2.0, 10.0, 20.0, 22, 0});
+    ASSERT_EQ(
+        configuration->get_window(1)->viewport_metrics().device_pixel_ratio,
+        2.0);
+    ASSERT_EQ(configuration->get_window(1)->viewport_metrics().physical_width,
+              10.0);
+    ASSERT_EQ(configuration->get_window(1)->viewport_metrics().physical_height,
+              20.0);
+    ASSERT_EQ(
+        configuration->get_window(1)->viewport_metrics().physical_touch_slop,
+        22);
+    ASSERT_NE(configuration->get_window(1), nullptr);
+    ASSERT_EQ(configuration->get_window(2), nullptr);
+
+    message_latch->Signal();
+  };
+
+  Settings settings = CreateSettingsForFixture();
+  TaskRunners task_runners("test",                  // label
+                           GetCurrentTaskRunner(),  // platform
+                           CreateNewThread(),       // raster
+                           CreateNewThread(),       // ui
+                           CreateNewThread()        // io
+  );
+
+  AddNativeCallback("ValidateConfiguration",
+                    CREATE_NATIVE_ENTRY(nativeValidateConfiguration));
+
+  std::unique_ptr<Shell> shell = CreateShell(settings, task_runners);
+
+  ASSERT_TRUE(shell->IsSetup());
+  auto run_configuration = RunConfiguration::InferFromSettings(settings);
+  run_configuration.SetEntrypoint("validateConfiguration");
+
+  shell->RunEngine(std::move(run_configuration), [&](auto result) {
+    ASSERT_EQ(result, Engine::RunStatus::Success);
+  });
+
+  message_latch->Wait();
+  DestroyShell(std::move(shell), task_runners);
+}
+
+TEST_F(PlatformConfigurationTest, OnErrorHandlesError) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   bool did_throw = false;
 
@@ -159,7 +213,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorHandlesError) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorDoesNotHandleError) {
+TEST_F(PlatformConfigurationTest, OnErrorDoesNotHandleError) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   std::string ex;
   std::string st;
@@ -211,7 +265,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorDoesNotHandleError) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorThrows) {
+TEST_F(PlatformConfigurationTest, OnErrorThrows) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   std::vector<std::string> errors;
   size_t throw_count = 0;
@@ -266,7 +320,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorThrows) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationSetDartPerformanceMode) {
+TEST_F(PlatformConfigurationTest, SetDartPerformanceMode) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   auto finish = [message_latch](Dart_NativeArguments args) {
     // call needs to happen on the UI thread.

From ad0a0d6165f889df0159841c498f953f6622d3d5 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Thu, 6 Jul 2023 09:55:47 -0700
Subject: [PATCH 08/17] Extractg get_window

---
 lib/ui/window/platform_configuration.cc | 9 +++++++++
 lib/ui/window/platform_configuration.h  | 9 +--------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/lib/ui/window/platform_configuration.cc b/lib/ui/window/platform_configuration.cc
index b1cd11fad30e7..fe6ff03d62b69 100644
--- a/lib/ui/window/platform_configuration.cc
+++ b/lib/ui/window/platform_configuration.cc
@@ -308,6 +308,15 @@ void PlatformConfiguration::ReportTimings(std::vector<int64_t> timings) {
                                                }));
 }
 
+Window* PlatformConfiguration::get_window(int window_id) {
+  auto found = windows_.find(window_id);
+  if (found != windows_.end()) {
+    return found->second.get();
+  } else {
+    return nullptr;
+  }
+}
+
 void PlatformConfiguration::CompletePlatformMessageEmptyResponse(
     int response_id) {
   if (!response_id) {
diff --git a/lib/ui/window/platform_configuration.h b/lib/ui/window/platform_configuration.h
index 77836717809e8..41a9708c814c8 100644
--- a/lib/ui/window/platform_configuration.h
+++ b/lib/ui/window/platform_configuration.h
@@ -415,14 +415,7 @@ class PlatformConfiguration final {
   ///
   /// @return     a pointer to the Window.
   ///
-  Window* get_window(int window_id) {
-    auto found = windows_.find(window_id);
-    if (found != windows_.end()) {
-      return found->second.get();
-    } else {
-      return nullptr;
-    }
-  }
+  Window* get_window(int window_id);
 
   //----------------------------------------------------------------------------
   /// @brief      Responds to a previous platform message to the engine from the

From d397d551a4eaa05168ed6b28129ddf0fa3c564bf Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Thu, 6 Jul 2023 10:19:48 -0700
Subject: [PATCH 09/17] Fix test

---
 lib/ui/window/platform_configuration.h        |  3 +-
 .../platform_configuration_unittests.cc       | 35 ++++++-------------
 2 files changed, 13 insertions(+), 25 deletions(-)

diff --git a/lib/ui/window/platform_configuration.h b/lib/ui/window/platform_configuration.h
index 41a9708c814c8..5722c1ce5a42f 100644
--- a/lib/ui/window/platform_configuration.h
+++ b/lib/ui/window/platform_configuration.h
@@ -413,7 +413,8 @@ class PlatformConfiguration final {
   ///
   /// @param[in] window_id The id of the window to find and return.
   ///
-  /// @return     a pointer to the Window.
+  /// @return     a pointer to the Window. Nullptr if the ID is not registered
+  ///             yet.
   ///
   Window* get_window(int window_id);
 
diff --git a/lib/ui/window/platform_configuration_unittests.cc b/lib/ui/window/platform_configuration_unittests.cc
index a9146790c2dc2..92cb0b8bcd1fa 100644
--- a/lib/ui/window/platform_configuration_unittests.cc
+++ b/lib/ui/window/platform_configuration_unittests.cc
@@ -19,6 +19,8 @@
 namespace flutter {
 namespace testing {
 
+class PlatformConfigurationTest : public ShellTest {};
+
 TEST_F(PlatformConfigurationTest, Initialization) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
@@ -113,34 +115,19 @@ TEST_F(PlatformConfigurationTest, WindowMetricsUpdate) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(PlatformConfigurationTest,
-       RegularWindowIsUnavailableUntilMetricsUpdate) {
+TEST_F(PlatformConfigurationTest, RegularWindowIsUnavailableAtStartup) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
-  auto nativeValidateConfiguration = [message_latch](
-                                         Dart_NativeArguments args) {
-    PlatformConfiguration* configuration =
-        UIDartState::Current()->platform_configuration();
+  auto nativeValidateConfiguration =
+      [message_latch](Dart_NativeArguments args) {
+        PlatformConfiguration* configuration =
+            UIDartState::Current()->platform_configuration();
 
-    // Non-implicit views should not be created at startup
-    ASSERT_EQ(configuration->get_window(1), nullptr);
-    configuration->get_window(1)->UpdateWindowMetrics(
-        ViewportMetrics{2.0, 10.0, 20.0, 22, 0});
-    ASSERT_EQ(
-        configuration->get_window(1)->viewport_metrics().device_pixel_ratio,
-        2.0);
-    ASSERT_EQ(configuration->get_window(1)->viewport_metrics().physical_width,
-              10.0);
-    ASSERT_EQ(configuration->get_window(1)->viewport_metrics().physical_height,
-              20.0);
-    ASSERT_EQ(
-        configuration->get_window(1)->viewport_metrics().physical_touch_slop,
-        22);
-    ASSERT_NE(configuration->get_window(1), nullptr);
-    ASSERT_EQ(configuration->get_window(2), nullptr);
+        ASSERT_EQ(configuration->get_window(1), nullptr);
+        ASSERT_EQ(configuration->get_window(2), nullptr);
 
-    message_latch->Signal();
-  };
+        message_latch->Signal();
+      };
 
   Settings settings = CreateSettingsForFixture();
   TaskRunners task_runners("test",                  // label

From 57e705e149d11376e4aedbec7e221591b5a34a3c Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 10:41:56 -0700
Subject: [PATCH 10/17] Back to current

---
 .../Headers/FlutterPluginRegistrarMacOS.h     | 23 +------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index d129f870ecb11..0a5ae5dd695a8 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -38,28 +38,7 @@ FLUTTER_DARWIN_EXPORT
 /**
  * The view displaying Flutter content.
  *
- * Currently Flutter only supports one view, and this is the view.
- *
- * Flutter plans to support multiple views in the future. Although single-view
- * APIs will eventually be replaced by their multi-view variants, during the
- * deprecation period, the single-view APIs will coexist with and work with the
- * multi-view APIs as if the other views don't exist. To achieve this,
- * all behaviors of "the single view" (which is called "the implicit view") are
- * preserved, allowing legacy single-view APIs to continue working, while
- * new-style views created by new ways must be operated by the upcoming
- * multi-view APIs.
- *
- * Plugins written for a single view can keep operating on this view and expect
- * unchanged behavior for the implicit view. This includes that:
- *
- *  - The first view controller attached to the engine will be linked to the
- *    implicit view.
- *  - Single-view Flutter APIs will operate the implicit view.
- *
- * This method may return |nil| if the view is not assigned. In single-view
- * apps, this means that the app is running headlessly. In multi-view apps,
- * this means that the compatible mode is disabled, or that the compatible mode
- * is on but no view controller has been attached to the engine yet.
+ * This method may return |nil|, for instance in a headless environment.
  */
 @property(nullable, readonly) NSView* view;
 

From 13764d791ec57306ffa7d0d3dd7b9fdff442be1f Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 10:49:18 -0700
Subject: [PATCH 11/17] More default->implicit

---
 shell/common/engine_unittests.cc              |  4 +-
 shell/common/shell_test.cc                    |  6 +--
 shell/common/shell_unittests.cc               | 38 +++++++++----------
 .../fuchsia/flutter/flatland_platform_view.cc |  4 +-
 .../fuchsia/flutter/gfx_platform_view.cc      |  4 +-
 shell/testing/tester_main.cc                  |  4 +-
 6 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/shell/common/engine_unittests.cc b/shell/common/engine_unittests.cc
index 995c408247ef4..d1a7d24d39cbc 100644
--- a/shell/common/engine_unittests.cc
+++ b/shell/common/engine_unittests.cc
@@ -21,7 +21,7 @@
 namespace flutter {
 
 namespace {
-constexpr int64_t kDefaultViewId = 0ll;
+constexpr int64_t kImplicitViewId = 0ll;
 
 class MockDelegate : public Engine::Delegate {
  public:
@@ -332,7 +332,7 @@ TEST_F(EngineTest, SpawnResetsViewportMetrics) {
     const double kViewHeight = 1024;
     old_viewport_metrics.physical_width = kViewWidth;
     old_viewport_metrics.physical_height = kViewHeight;
-    mock_runtime_controller->SetViewportMetrics(kDefaultViewId,
+    mock_runtime_controller->SetViewportMetrics(kImplicitViewId,
                                                 old_viewport_metrics);
     auto engine = std::make_unique<Engine>(
         /*delegate=*/delegate_,
diff --git a/shell/common/shell_test.cc b/shell/common/shell_test.cc
index b892faefcef84..1ea8c7f0b3248 100644
--- a/shell/common/shell_test.cc
+++ b/shell/common/shell_test.cc
@@ -20,7 +20,7 @@
 namespace flutter {
 namespace testing {
 
-constexpr int64_t kDefaultViewId = 0;
+constexpr int64_t kImplicitViewId = 0;
 
 ShellTest::ShellTest()
     : thread_host_("io.flutter.test." + GetCurrentTestName() + ".",
@@ -146,7 +146,7 @@ void ShellTest::SetViewportMetrics(Shell* shell, double width, double height) {
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
         if (engine) {
-          engine->SetViewportMetrics(kDefaultViewId, viewport_metrics);
+          engine->SetViewportMetrics(kImplicitViewId, viewport_metrics);
           const auto frame_begin_time = fml::TimePoint::Now();
           const auto frame_end_time =
               frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);
@@ -188,7 +188,7 @@ void ShellTest::PumpOneFrame(Shell* shell,
   fml::AutoResetWaitableEvent latch;
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
-        engine->SetViewportMetrics(kDefaultViewId, viewport_metrics);
+        engine->SetViewportMetrics(kImplicitViewId, viewport_metrics);
         const auto frame_begin_time = fml::TimePoint::Now();
         const auto frame_end_time =
             frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);
diff --git a/shell/common/shell_unittests.cc b/shell/common/shell_unittests.cc
index e9c606b704743..c96f525777291 100644
--- a/shell/common/shell_unittests.cc
+++ b/shell/common/shell_unittests.cc
@@ -60,7 +60,7 @@
 namespace flutter {
 namespace testing {
 
-constexpr int64_t kDefaultViewId = 0ll;
+constexpr int64_t kImplicitViewId = 0ll;
 
 using ::testing::_;
 using ::testing::Return;
@@ -1639,7 +1639,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
 
   RunEngine(shell.get(), std::move(configuration));
   PostSync(shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                  {1.0, 100, 100, 22, 0});
   });
 
@@ -1669,7 +1669,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 kDefaultViewId, {1.0, 100, 100, 22, 0});
+                 kImplicitViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1678,7 +1678,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 kDefaultViewId, {1.0, 100, 300, 22, 0});
+                 kImplicitViewId, {1.0, 100, 300, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1689,7 +1689,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 kDefaultViewId, {1.0, 400, 100, 22, 0});
+                 kImplicitViewId, {1.0, 400, 100, 22, 0});
            });
   // first cache bytes + second cache bytes + third cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1698,7 +1698,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 kDefaultViewId, {1.0, 800, 100, 22, 0});
+                 kImplicitViewId, {1.0, 800, 100, 22, 0});
            });
   // max bytes threshold
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1711,7 +1711,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 kDefaultViewId, {1.0, 100, 100, 22, 0});
+                 kImplicitViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1755,7 +1755,7 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
@@ -1776,7 +1776,7 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {1.0, 800, 400, 22, 0});
       });
   PumpOneFrame(shell.get());
@@ -1794,7 +1794,7 @@ TEST_F(ShellTest, SetResourceCacheSizeEarly) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
@@ -1822,7 +1822,7 @@ TEST_F(ShellTest, SetResourceCacheSizeNotifiesDart) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
@@ -2690,7 +2690,7 @@ TEST_F(ShellTest, DISABLED_DiscardLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &expected_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            kDefaultViewId,
+            kImplicitViewId,
             {1.0, static_cast<double>(expected_size.width()),
              static_cast<double>(expected_size.height()), 22, 0});
       });
@@ -2768,7 +2768,7 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &origin_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            kDefaultViewId, {1.0, static_cast<double>(origin_size.width()),
+            kImplicitViewId, {1.0, static_cast<double>(origin_size.width()),
                              static_cast<double>(origin_size.height()), 22, 0});
       });
 
@@ -2787,7 +2787,7 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &new_size, &resize_latch]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            kDefaultViewId, {1.0, static_cast<double>(new_size.width()),
+            kImplicitViewId, {1.0, static_cast<double>(new_size.width()),
                              static_cast<double>(new_size.height()), 22, 0});
         resize_latch.Signal();
       });
@@ -2851,17 +2851,17 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   RunEngine(shell.get(), std::move(configuration));
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                  {0.0, 400, 200, 22, 0});
     task_runner->PostTask([&]() {
-      shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+      shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                    {0.8, 0.0, 200, 22, 0});
       task_runner->PostTask([&]() {
-        shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {0.8, 400, 0.0, 22, 0});
         task_runner->PostTask([&]() {
           shell->GetPlatformView()->SetViewportMetrics(
-              kDefaultViewId, {0.8, 400, 200.0, 22, 0});
+              kImplicitViewId, {0.8, 400, 200.0, 22, 0});
         });
       });
     });
@@ -2873,7 +2873,7 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   latch.Reset();
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId,
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                  {1.2, 600, 300, 22, 0});
   });
   latch.Wait();
diff --git a/shell/platform/fuchsia/flutter/flatland_platform_view.cc b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
index e9c55f87f539e..e7c4067210a2e 100644
--- a/shell/platform/fuchsia/flutter/flatland_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
@@ -8,7 +8,7 @@
 
 namespace flutter_runner {
 
-static constexpr int64_t kFlutterDefaultViewId = 0ll;
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
 
 FlatlandPlatformView::FlatlandPlatformView(
     flutter::PlatformView::Delegate& delegate,
@@ -87,7 +87,7 @@ void FlatlandPlatformView::OnGetLayout(
 
   float pixel_ratio = view_pixel_ratio_ ? *view_pixel_ratio_ : 1.0f;
 
-  SetViewportMetrics(kFlutterDefaultViewId,
+  SetViewportMetrics(kFlutterImplicitViewId,
                      {
                          pixel_ratio,  // device_pixel_ratio
                          std::round(view_logical_size_.value()[0] *
diff --git a/shell/platform/fuchsia/flutter/gfx_platform_view.cc b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
index 149e91d7135af..a951938e390d6 100644
--- a/shell/platform/fuchsia/flutter/gfx_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
@@ -8,7 +8,7 @@
 
 namespace flutter_runner {
 
-static constexpr int64_t kFlutterDefaultViewId = 0ll;
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
 
 GfxPlatformView::GfxPlatformView(
     flutter::PlatformView::Delegate& delegate,
@@ -216,7 +216,7 @@ void GfxPlatformView::OnScenicEvent(
     const float pixel_ratio = *view_pixel_ratio_;
     const std::array<float, 2> logical_size = *view_logical_size_;
     SetViewportMetrics(
-        kFlutterDefaultViewId,
+        kFlutterImplicitViewId,
         {
             pixel_ratio,                                // device_pixel_ratio
             std::round(logical_size[0] * pixel_ratio),  // physical_width
diff --git a/shell/testing/tester_main.cc b/shell/testing/tester_main.cc
index a6719ede8ffdf..3bb48710c8bb1 100644
--- a/shell/testing/tester_main.cc
+++ b/shell/testing/tester_main.cc
@@ -39,7 +39,7 @@
 
 namespace flutter {
 
-static constexpr int64_t kDefaultViewId = 0ll;
+static constexpr int64_t kImplicitViewId = 0ll;
 
 class TesterExternalViewEmbedder : public ExternalViewEmbedder {
   // |ExternalViewEmbedder|
@@ -355,7 +355,7 @@ int RunTester(const flutter::Settings& settings,
   metrics.physical_width = physical_width;
   metrics.physical_height = physical_height;
   metrics.display_id = 0;
-  shell->GetPlatformView()->SetViewportMetrics(kDefaultViewId, metrics);
+  shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId, metrics);
 
   // Run the message loop and wait for the script to do its thing.
   fml::MessageLoop::GetCurrent().Run();

From a71e5b582b556227c2d6273d07eba3cc43162c7e Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@users.noreply.github.com>
Date: Fri, 7 Jul 2023 10:56:41 -0700
Subject: [PATCH 12/17] Update FlutterPluginRegistrarMacOS.h

---
 .../macos/framework/Headers/FlutterPluginRegistrarMacOS.h     | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
index 0a5ae5dd695a8..86746c8bb30e1 100644
--- a/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
+++ b/shell/platform/darwin/macos/framework/Headers/FlutterPluginRegistrarMacOS.h
@@ -38,6 +38,10 @@ FLUTTER_DARWIN_EXPORT
 /**
  * The view displaying Flutter content.
  *
+ * This property is provided for backwards compatibility for apps
+ * that assume a single view. This will eventually be replaced by
+ * a multi-view API variant.
+ *
  * This method may return |nil|, for instance in a headless environment.
  */
 @property(nullable, readonly) NSView* view;

From 65171322aebe3a60321cfe8a35db3bac1edf63c0 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 11:52:18 -0700
Subject: [PATCH 13/17] Format

---
 shell/common/shell_unittests.cc | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/shell/common/shell_unittests.cc b/shell/common/shell_unittests.cc
index 7a1d7f4621c64..ce9feb8b4c6a8 100644
--- a/shell/common/shell_unittests.cc
+++ b/shell/common/shell_unittests.cc
@@ -2768,8 +2768,9 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &origin_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            kImplicitViewId, {1.0, static_cast<double>(origin_size.width()),
-                             static_cast<double>(origin_size.height()), 22, 0});
+            kImplicitViewId,
+            {1.0, static_cast<double>(origin_size.width()),
+             static_cast<double>(origin_size.height()), 22, 0});
       });
 
   auto configuration = RunConfiguration::InferFromSettings(settings);
@@ -2788,7 +2789,7 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       [&shell, &new_size, &resize_latch]() {
         shell->GetPlatformView()->SetViewportMetrics(
             kImplicitViewId, {1.0, static_cast<double>(new_size.width()),
-                             static_cast<double>(new_size.height()), 22, 0});
+                              static_cast<double>(new_size.height()), 22, 0});
         resize_latch.Signal();
       });
 

From 19f24b213719f2be1ab452ddf86a861e57500052 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 12:04:25 -0700
Subject: [PATCH 14/17] Update parameter docs

---
 lib/ui/window/platform_configuration_unittests.cc |  2 +-
 runtime/runtime_controller.h                      |  1 +
 shell/common/engine.h                             | 10 +++++-----
 shell/common/platform_view.h                      | 15 ++++++++-------
 4 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/lib/ui/window/platform_configuration_unittests.cc b/lib/ui/window/platform_configuration_unittests.cc
index 92cb0b8bcd1fa..017055a41d91e 100644
--- a/lib/ui/window/platform_configuration_unittests.cc
+++ b/lib/ui/window/platform_configuration_unittests.cc
@@ -115,7 +115,7 @@ TEST_F(PlatformConfigurationTest, WindowMetricsUpdate) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(PlatformConfigurationTest, RegularWindowIsUnavailableAtStartup) {
+TEST_F(PlatformConfigurationTest, GetWindowReturnsNullForNonexistentId) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
   auto nativeValidateConfiguration =
diff --git a/runtime/runtime_controller.h b/runtime/runtime_controller.h
index b4b1fcc8d3c8d..aaef6da631694 100644
--- a/runtime/runtime_controller.h
+++ b/runtime/runtime_controller.h
@@ -168,6 +168,7 @@ class RuntimeController : public PlatformConfigurationClient {
   ///             If the isolate is not running, these metrics will be saved and
   ///             flushed to the isolate when it starts.
   ///
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
   /// @param[in]  metrics  The window's viewport metrics.
   ///
   /// @return     If the window metrics were forwarded to the running isolate.
diff --git a/shell/common/engine.h b/shell/common/engine.h
index d141ffa0cc28a..ca258ac392159 100644
--- a/shell/common/engine.h
+++ b/shell/common/engine.h
@@ -677,14 +677,14 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   std::optional<uint32_t> GetUIIsolateReturnCode();
 
   //----------------------------------------------------------------------------
-  /// @brief      Updates the viewport metrics for the currently running Flutter
-  ///             application. The viewport metrics detail the size of the
-  ///             rendering viewport in texels as well as edge insets if
-  ///             present.
+  /// @brief      Updates the viewport metrics for a view. The viewport metrics
+  ///             detail the size of the rendering viewport in texels as well as
+  ///             edge insets if present.
   ///
   /// @see        `ViewportMetrics`
   ///
-  /// @param[in]  metrics  The metrics
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
+  /// @param[in]  metrics  The metrics.
   ///
   void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
diff --git a/shell/common/platform_view.h b/shell/common/platform_view.h
index 3e5aab515ccd8..e6c7dab924e5c 100644
--- a/shell/common/platform_view.h
+++ b/shell/common/platform_view.h
@@ -104,11 +104,11 @@ class PlatformView {
         const fml::closure& closure) = 0;
 
     //--------------------------------------------------------------------------
-    /// @brief      Notifies the delegate the viewport metrics of the platform
-    ///             view have been updated. The rasterizer will need to be
-    ///             reconfigured to render the frame in the updated viewport
-    ///             metrics.
+    /// @brief      Notifies the delegate the viewport metrics of a view have
+    ///             been updated. The rasterizer will need to be reconfigured to
+    ///             render the frame in the updated viewport metrics.
     ///
+    /// @param[in]  view_id  The ID for the view that `metrics` describes.
     /// @param[in]  metrics  The updated viewport metrics.
     ///
     virtual void OnPlatformViewSetViewportMetrics(
@@ -466,13 +466,14 @@ class PlatformView {
                                CustomAccessibilityActionUpdates actions);
 
   //----------------------------------------------------------------------------
-  /// @brief      Used by embedders to specify the updated viewport metrics. In
-  ///             response to this call, on the raster thread, the rasterizer
-  ///             may need to be reconfigured to the updated viewport
+  /// @brief      Used by embedders to specify the updated viewport metrics for
+  ///             a view. In response to this call, on the raster thread, the
+  ///             rasterizer may need to be reconfigured to the updated viewport
   ///             dimensions. On the UI thread, the framework may need to start
   ///             generating a new frame for the updated viewport metrics as
   ///             well.
   ///
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
   /// @param[in]  metrics  The updated viewport metrics.
   ///
   void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);

From 73790caccfb4acf48b29e401f8c83212c7e8b03a Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 12:07:09 -0700
Subject: [PATCH 15/17] Fix format for fuchsia

---
 .../fuchsia/flutter/flatland_platform_view.cc | 51 +++++++++----------
 .../fuchsia/flutter/gfx_platform_view.cc      | 47 +++++++++--------
 2 files changed, 48 insertions(+), 50 deletions(-)

diff --git a/shell/platform/fuchsia/flutter/flatland_platform_view.cc b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
index e7c4067210a2e..39febd8c6db64 100644
--- a/shell/platform/fuchsia/flutter/flatland_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/flatland_platform_view.cc
@@ -86,32 +86,31 @@ void FlatlandPlatformView::OnGetLayout(
   }
 
   float pixel_ratio = view_pixel_ratio_ ? *view_pixel_ratio_ : 1.0f;
-
-  SetViewportMetrics(kFlutterImplicitViewId,
-                     {
-                         pixel_ratio,  // device_pixel_ratio
-                         std::round(view_logical_size_.value()[0] *
-                                    pixel_ratio),  // physical_width
-                         std::round(view_logical_size_.value()[1] *
-                                    pixel_ratio),  // physical_height
-                         0.0f,                     // physical_padding_top
-                         0.0f,                     // physical_padding_right
-                         0.0f,                     // physical_padding_bottom
-                         0.0f,                     // physical_padding_left
-                         0.0f,                     // physical_view_inset_top
-                         0.0f,                     // physical_view_inset_right
-                         0.0f,                     // physical_view_inset_bottom
-                         0.0f,                     // physical_view_inset_left
-                         0.0f,  // p_physical_system_gesture_inset_top
-                         0.0f,  // p_physical_system_gesture_inset_right
-                         0.0f,  // p_physical_system_gesture_inset_bottom
-                         0.0f,  // p_physical_system_gesture_inset_left,
-                         -1.0,  // p_physical_touch_slop,
-                         {},    // p_physical_display_features_bounds
-                         {},    // p_physical_display_features_type
-                         {},    // p_physical_display_features_state
-                         0,     // p_display_id
-                     });
+  flutter::ViewportMetrics metrics{
+      pixel_ratio,  // device_pixel_ratio
+      std::round(view_logical_size_.value()[0] *
+                 pixel_ratio),  // physical_width
+      std::round(view_logical_size_.value()[1] *
+                 pixel_ratio),  // physical_height
+      0.0f,                     // physical_padding_top
+      0.0f,                     // physical_padding_right
+      0.0f,                     // physical_padding_bottom
+      0.0f,                     // physical_padding_left
+      0.0f,                     // physical_view_inset_top
+      0.0f,                     // physical_view_inset_right
+      0.0f,                     // physical_view_inset_bottom
+      0.0f,                     // physical_view_inset_left
+      0.0f,                     // p_physical_system_gesture_inset_top
+      0.0f,                     // p_physical_system_gesture_inset_right
+      0.0f,                     // p_physical_system_gesture_inset_bottom
+      0.0f,                     // p_physical_system_gesture_inset_left,
+      -1.0,                     // p_physical_touch_slop,
+      {},                       // p_physical_display_features_bounds
+      {},                       // p_physical_display_features_type
+      {},                       // p_physical_display_features_state
+      0,                        // p_display_id
+  };
+  SetViewportMetrics(kFlutterImplicitViewId, metrics);
 
   parent_viewport_watcher_->GetLayout(
       fit::bind_member(this, &FlatlandPlatformView::OnGetLayout));
diff --git a/shell/platform/fuchsia/flutter/gfx_platform_view.cc b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
index a951938e390d6..ddb0ce029e2a1 100644
--- a/shell/platform/fuchsia/flutter/gfx_platform_view.cc
+++ b/shell/platform/fuchsia/flutter/gfx_platform_view.cc
@@ -215,30 +215,29 @@ void GfxPlatformView::OnScenicEvent(
       metrics_changed) {
     const float pixel_ratio = *view_pixel_ratio_;
     const std::array<float, 2> logical_size = *view_logical_size_;
-    SetViewportMetrics(
-        kFlutterImplicitViewId,
-        {
-            pixel_ratio,                                // device_pixel_ratio
-            std::round(logical_size[0] * pixel_ratio),  // physical_width
-            std::round(logical_size[1] * pixel_ratio),  // physical_height
-            0.0f,                                       // physical_padding_top
-            0.0f,  // physical_padding_right
-            0.0f,  // physical_padding_bottom
-            0.0f,  // physical_padding_left
-            0.0f,  // physical_view_inset_top
-            0.0f,  // physical_view_inset_right
-            0.0f,  // physical_view_inset_bottom
-            0.0f,  // physical_view_inset_left
-            0.0f,  // p_physical_system_gesture_inset_top
-            0.0f,  // p_physical_system_gesture_inset_right
-            0.0f,  // p_physical_system_gesture_inset_bottom
-            0.0f,  // p_physical_system_gesture_inset_left,
-            -1.0,  // p_physical_touch_slop,
-            {},    // p_physical_display_features_bounds
-            {},    // p_physical_display_features_type
-            {},    // p_physical_display_features_state
-            0,     // pdisplay_id
-        });
+    flutter::ViewportMetrics metrics{
+        pixel_ratio,                                // device_pixel_ratio
+        std::round(logical_size[0] * pixel_ratio),  // physical_width
+        std::round(logical_size[1] * pixel_ratio),  // physical_height
+        0.0f,                                       // physical_padding_top
+        0.0f,                                       // physical_padding_right
+        0.0f,                                       // physical_padding_bottom
+        0.0f,                                       // physical_padding_left
+        0.0f,                                       // physical_view_inset_top
+        0.0f,                                       // physical_view_inset_right
+        0.0f,  // physical_view_inset_bottom
+        0.0f,  // physical_view_inset_left
+        0.0f,  // p_physical_system_gesture_inset_top
+        0.0f,  // p_physical_system_gesture_inset_right
+        0.0f,  // p_physical_system_gesture_inset_bottom
+        0.0f,  // p_physical_system_gesture_inset_left,
+        -1.0,  // p_physical_touch_slop,
+        {},    // p_physical_display_features_bounds
+        {},    // p_physical_display_features_type
+        {},    // p_physical_display_features_state
+        0,     // pdisplay_id
+    };
+    SetViewportMetrics(kFlutterImplicitViewId, metrics);
   }
 }
 

From 4b57af3b2ad61d8ff652f0d929f25e24145a44de Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 13:32:33 -0700
Subject: [PATCH 16/17] Address feedback

---
 shell/common/shell.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/shell/common/shell.cc b/shell/common/shell.cc
index 23de5bea8f0fd..82b3b831ebb68 100644
--- a/shell/common/shell.cc
+++ b/shell/common/shell.cc
@@ -979,7 +979,7 @@ void Shell::OnPlatformViewSetViewportMetrics(int64_t view_id,
       });
 
   task_runners_.GetUITaskRunner()->PostTask(
-      [engine = engine_->GetWeakPtr(), metrics, view_id]() {
+      [engine = engine_->GetWeakPtr(), view_id, metrics]() {
         if (engine) {
           engine->SetViewportMetrics(view_id, metrics);
         }

From f3cb395c778ae23e282f3a93a1afc509ec172023 Mon Sep 17 00:00:00 2001
From: Tong Mu <dkwingsmt@gmail.com>
Date: Fri, 7 Jul 2023 14:34:09 -0700
Subject: [PATCH 17/17] Add test IgnoresMetricsUpdateToInvalidView

---
 runtime/runtime_controller.cc   |  2 ++
 shell/common/shell_unittests.cc | 50 +++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/runtime/runtime_controller.cc b/runtime/runtime_controller.cc
index 9cc704a8e7077..751fa696a5719 100644
--- a/runtime/runtime_controller.cc
+++ b/runtime/runtime_controller.cc
@@ -138,6 +138,8 @@ bool RuntimeController::SetViewportMetrics(int64_t view_id,
     if (window) {
       window->UpdateWindowMetrics(metrics);
       return true;
+    } else {
+      FML_LOG(WARNING) << "View ID " << view_id << " does not exist.";
     }
   }
 
diff --git a/shell/common/shell_unittests.cc b/shell/common/shell_unittests.cc
index ce9feb8b4c6a8..4c4c85f8b768b 100644
--- a/shell/common/shell_unittests.cc
+++ b/shell/common/shell_unittests.cc
@@ -2852,15 +2852,19 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   RunEngine(shell.get(), std::move(configuration));
 
   task_runner->PostTask([&]() {
+    // This one is invalid for having 0 pixel ratio.
     shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                  {0.0, 400, 200, 22, 0});
     task_runner->PostTask([&]() {
+      // This one is invalid for having 0 width.
       shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                    {0.8, 0.0, 200, 22, 0});
       task_runner->PostTask([&]() {
+        // This one is invalid for having 0 height.
         shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
                                                      {0.8, 400, 0.0, 22, 0});
         task_runner->PostTask([&]() {
+          // This one makes it through.
           shell->GetPlatformView()->SetViewportMetrics(
               kImplicitViewId, {0.8, 400, 200.0, 22, 0});
         });
@@ -2885,6 +2889,52 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   DestroyShell(std::move(shell), task_runners);
 }
 
+TEST_F(ShellTest, IgnoresMetricsUpdateToInvalidView) {
+  fml::AutoResetWaitableEvent latch;
+  double last_device_pixel_ratio;
+  // This callback will be called whenever any view's metrics change.
+  auto native_report_device_pixel_ratio = [&](Dart_NativeArguments args) {
+    // The correct call will have a DPR of 3.
+    auto dpr_handle = Dart_GetNativeArgument(args, 0);
+    ASSERT_TRUE(Dart_IsDouble(dpr_handle));
+    Dart_DoubleValue(dpr_handle, &last_device_pixel_ratio);
+    ASSERT_TRUE(last_device_pixel_ratio > 2.5);
+
+    latch.Signal();
+  };
+
+  Settings settings = CreateSettingsForFixture();
+  auto task_runner = CreateNewThread();
+  TaskRunners task_runners("test", task_runner, task_runner, task_runner,
+                           task_runner);
+
+  AddNativeCallback("ReportMetrics",
+                    CREATE_NATIVE_ENTRY(native_report_device_pixel_ratio));
+
+  std::unique_ptr<Shell> shell = CreateShell(settings, task_runners);
+
+  auto configuration = RunConfiguration::InferFromSettings(settings);
+  configuration.SetEntrypoint("reportMetrics");
+
+  RunEngine(shell.get(), std::move(configuration));
+
+  task_runner->PostTask([&]() {
+    // This one is invalid for having an nonexistent view ID.
+    // Also, it has a DPR of 2.0 for detection.
+    shell->GetPlatformView()->SetViewportMetrics(2, {2.0, 400, 200, 22, 0});
+    task_runner->PostTask([&]() {
+      // This one is valid with DPR 3.0.
+      shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                   {3.0, 400, 200, 22, 0});
+    });
+  });
+  latch.Wait();
+  ASSERT_EQ(last_device_pixel_ratio, 3.0);
+  latch.Reset();
+
+  DestroyShell(std::move(shell), task_runners);
+}
+
 TEST_F(ShellTest, OnServiceProtocolSetAssetBundlePathWorks) {
   Settings settings = CreateSettingsForFixture();
   std::unique_ptr<Shell> shell = CreateShell(settings);