[flutter_runner] Refactor thread_application pair to ActiveApplication

shell/platform/fuchsia/flutter/component.cc

@@ -38,8 +38,7 @@ constexpr char kDataKey[] = "data";
 constexpr char kTmpPath[] = "/tmp";
 constexpr char kServiceRootPath[] = "/svc";
 
-std::pair<std::unique_ptr<Thread>, std::unique_ptr<Application>>
-Application::Create(
+ActiveApplication Application::Create(
     TerminationCallback termination_callback,
     fuchsia::sys::Package package,
     fuchsia::sys::StartupInfo startup_info,
@@ -58,7 +57,7 @@ Application::Create(
   });
 
   latch.Wait();
-  return {std::move(thread), std::move(application)};
+  return {.thread = std::move(thread), .application = std::move(application)};
 }
 
 static std::string DebugLabelForURL(const std::string& url) {

shell/platform/fuchsia/flutter/component.h

@@ -30,6 +30,23 @@
 
 namespace flutter_runner {
 
+class Application;
+
+struct ActiveApplication {
+  std::unique_ptr<Thread> thread;
+  std::unique_ptr<Application> application;
+
+  ActiveApplication& operator=(ActiveApplication&& other) noexcept {
+    if (this != &other) {
+      this->thread.reset(other.thread.release());
+      this->application.reset(other.application.release());
+    }
+    return *this;
+  }
+
+  ~ActiveApplication() = default;
+};
+
 // Represents an instance of a Flutter application that contains one of more
 // Flutter engine instances.
 class Application final : public Engine::Delegate,
@@ -41,12 +58,12 @@ class Application final : public Engine::Delegate,
   // Creates a dedicated thread to run the application and constructions the
   // application on it. The application can be accessed only on this thread.
   // This is a synchronous operation.
-  static std::pair<std::unique_ptr<Thread>, std::unique_ptr<Application>>
-  Create(TerminationCallback termination_callback,
-         fuchsia::sys::Package package,
-         fuchsia::sys::StartupInfo startup_info,
-         std::shared_ptr<sys::ServiceDirectory> runner_incoming_services,
-         fidl::InterfaceRequest<fuchsia::sys::ComponentController> controller);
+  static ActiveApplication Create(
+      TerminationCallback termination_callback,
+      fuchsia::sys::Package package,
+      fuchsia::sys::StartupInfo startup_info,
+      std::shared_ptr<sys::ServiceDirectory> runner_incoming_services,
+      fidl::InterfaceRequest<fuchsia::sys::ComponentController> controller);
 
   // Must be called on the same thread returned from the create call. The thread
   // may be collected after.

shell/platform/fuchsia/flutter/runner.cc

@@ -178,17 +178,16 @@ void Runner::StartComponent(
         });
       };
 
-  auto thread_application_pair = Application::Create(
+  auto active_application = Application::Create(
       std::move(termination_callback),  // termination callback
       std::move(package),               // application package
       std::move(startup_info),          // startup info
       context_->svc(),                  // runner incoming services
       std::move(controller)             // controller request
   );
 
-  auto key = thread_application_pair.second.get();
-
-  active_applications_[key] = std::move(thread_application_pair);
+  auto key = active_application.application.get();
+  active_applications_[key] = std::move(active_application);
 }
 
 void Runner::OnApplicationTerminate(const Application* application) {

shell/platform/fuchsia/flutter/runner.h

@@ -18,7 +18,6 @@
 #include "flutter/fml/macros.h"
 #include "lib/fidl/cpp/binding_set.h"
 #include "runtime/dart/utils/vmservice_object.h"
-#include "thread.h"
 
 namespace flutter_runner {
 
@@ -33,17 +32,6 @@ class Runner final : public fuchsia::sys::Runner {
  private:
   async::Loop* loop_;
 
-  struct ActiveApplication {
-    std::unique_ptr<Thread> thread;
-    std::unique_ptr<Application> application;
-
-    ActiveApplication(
-        std::pair<std::unique_ptr<Thread>, std::unique_ptr<Application>> pair)
-        : thread(std::move(pair.first)), application(std::move(pair.second)) {}
-
-    ActiveApplication() = default;
-  };
-
   std::unique_ptr<sys::ComponentContext> context_;
   fidl::BindingSet<fuchsia::sys::Runner> active_applications_bindings_;
   std::unordered_map<const Application*, ActiveApplication>