Discard embedded UIViews on hot restart.

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -152,6 +152,18 @@
   return canvas;
 }
 
+void FlutterPlatformViewsController::Reset() {
+  UIView* flutter_view = flutter_view_.get();
+  for (UIView* sub_view in [flutter_view subviews]) {
+    [sub_view removeFromSuperview];
+  }
+  views_.clear();
+  overlays_.clear();
+  composition_order_.clear();
+  active_composition_order_.clear();
+  composition_frames_.clear();
+}
+
 bool FlutterPlatformViewsController::Present() {
   bool did_submit = true;
   for (size_t i = 0; i < composition_frames_.size(); i++) {

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -53,6 +53,9 @@ class FlutterPlatformViewsController {
                                   const flow::EmbeddedViewParams& params,
                                   IOSSurface& surface);
 
+  // Discards all platform views instances and auxiliary resources.
+  void Reset();
+
   bool Present();
 
   void OnMethodCall(FlutterMethodCall* call, FlutterResult& result);

shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -31,7 +31,6 @@ @implementation FlutterViewController {
   fml::scoped_nsobject<FlutterView> _flutterView;
   fml::scoped_nsobject<UIView> _splashScreenView;
   fml::ScopedBlock<void (^)(void)> _flutterViewRenderedCallback;
-  std::unique_ptr<shell::FlutterPlatformViewsController> _platformViewsController;
   UIInterfaceOrientationMask _orientationPreferences;
   UIStatusBarStyle _statusBarStyle;
   blink::ViewportMetrics _viewportMetrics;
@@ -891,7 +890,7 @@ - (void)onPreferredStatusBarStyleUpdated:(NSNotification*)notification {
 #pragma mark - Platform views
 
 - (shell::FlutterPlatformViewsController*)platformViewsController {
-  return _platformViewsController.get();
+  return [_engine.get() platformViewsController];
 }
 
 #pragma mark - FlutterBinaryMessenger

shell/platform/darwin/ios/platform_view_ios.h

@@ -70,6 +70,9 @@ class PlatformViewIOS final : public PlatformView {
   // |shell::PlatformView|
   std::unique_ptr<VsyncWaiter> CreateVSyncWaiter() override;
 
+  // |shell::PlatformView|
+  void OnPreEngineRestart() const override;
+
   FML_DISALLOW_COPY_AND_ASSIGN(PlatformViewIOS);
 };
 

shell/platform/darwin/ios/platform_view_ios.mm

@@ -12,6 +12,7 @@
 #include "flutter/fml/synchronization/waitable_event.h"
 #include "flutter/fml/trace_event.h"
 #include "flutter/shell/common/io_manager.h"
+#include "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #include "flutter/shell/platform/darwin/ios/framework/Source/vsync_waiter_ios.h"
 #include "flutter/shell/platform/darwin/ios/ios_external_texture_gl.h"
 
@@ -118,6 +119,13 @@
   return std::make_unique<VsyncWaiterIOS>(task_runners_);
 }
 
+void PlatformViewIOS::OnPreEngineRestart() const {
+  if (!owner_controller_) {
+    return;
+  }
+  [owner_controller_.get() platformViewsController] -> Reset();
+}
+
 fml::scoped_nsprotocol<FlutterTextInputPlugin*> PlatformViewIOS::GetTextInputPlugin() const {
   return text_input_plugin_;
 }