Flush all embedded Android view on hot restart.

Adds an OnEngineRestarted method to PlatformView, this is currently only
implemented for Android where we need to use it for embedded views.

Author: amirh

shell/common/engine.cc

@@ -103,6 +103,7 @@ bool Engine::Restart(RunConfiguration configuration) {
   }
   runtime_controller_ = runtime_controller_->Clone();
   UpdateAssetManager(nullptr);
+  delegate_.OnEngineRestart();
   return Run(std::move(configuration));
 }
 

shell/common/engine.h

@@ -39,6 +39,8 @@ class Engine final : public blink::RuntimeDelegate {
     virtual void OnEngineHandlePlatformMessage(
         const Engine& engine,
         fml::RefPtr<blink::PlatformMessage> message) = 0;
+
+    virtual void OnEngineRestart() = 0;
   };
 
   Engine(Delegate& delegate,

shell/common/platform_view.cc

@@ -88,6 +88,8 @@ void PlatformView::HandlePlatformMessage(
     response->CompleteEmpty();
 }
 
+void PlatformView::OnEngineRestart() const {}
+
 void PlatformView::RegisterTexture(std::shared_ptr<flow::Texture> texture) {
   delegate_.OnPlatformViewRegisterTexture(*this, std::move(texture));
 }

shell/common/platform_view.h

@@ -108,6 +108,8 @@ class PlatformView {
   virtual void HandlePlatformMessage(
       fml::RefPtr<blink::PlatformMessage> message);
 
+  virtual void OnEngineRestart() const;
+
   void SetNextFrameCallback(fml::closure closure);
 
   void DispatchPointerDataPacket(

shell/common/shell.cc

@@ -740,6 +740,21 @@ void Shell::OnEngineHandlePlatformMessage(
       });
 }
 
+// |shell::Engine::Delegate|
+void Shell::OnEngineRestart() {
+  fml::AutoResetWaitableEvent latch;
+  task_runners_.GetPlatformTaskRunner()->PostTask(
+      [view = platform_view_->GetWeakPtr(), &latch] {
+        if (view) {
+          view->OnEngineRestart();
+        }
+        latch.Signal();
+      });
+  // This is blocking as any embedded platform views has to be flushed before
+  // we re-run the Dart code.
+  latch.Wait();
+}
+
 // |blink::ServiceProtocol::Handler|
 fml::RefPtr<fml::TaskRunner> Shell::GetServiceProtocolHandlerTaskRunner(
     fml::StringView method) const {

shell/common/shell.h

@@ -195,6 +195,9 @@ class Shell final : public PlatformView::Delegate,
       const Engine& engine,
       fml::RefPtr<blink::PlatformMessage> message) override;
 
+  // |shell::Engine::Delegate|
+  void OnEngineRestart() override;
+
   // |blink::ServiceProtocol::Handler|
   fml::RefPtr<fml::TaskRunner> GetServiceProtocolHandlerTaskRunner(
       fml::StringView method) const override;

shell/platform/android/io/flutter/app/FlutterPluginRegistry.java

@@ -82,6 +82,10 @@ public void detach() {
         mActivity = null;
     }
 
+    public void onEngineRestart() {
+        mPlatformViewsController.onEngineRestart();
+    }
+
     private class FlutterRegistrar implements Registrar {
         private final String pluginKey;
 

shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java

@@ -69,10 +69,11 @@ public PlatformViewRegistry getRegistry() {
     }
 
     public void onFlutterViewDestroyed() {
-        for (VirtualDisplayController controller : vdControllers.values()) {
-            controller.dispose();
-        }
-        vdControllers.clear();
+        flushAllViews();
+    }
+
+    public void onEngineRestart() {
+        flushAllViews();
     }
 
     @Override
@@ -297,4 +298,10 @@ private int toPhysicalPixels(double logicalPixels) {
         return (int) Math.round(logicalPixels * density);
     }
 
+    private void flushAllViews() {
+        for (VirtualDisplayController controller : vdControllers.values()) {
+            controller.dispose();
+        }
+        vdControllers.clear();
+    }
 }

shell/platform/android/io/flutter/view/FlutterNativeView.java

@@ -198,6 +198,14 @@ private void onFirstFrame() {
         mFlutterView.onFirstFrame();
     }
 
+    // Called by native to notify when the engine is restarted (cold reload).
+    @SuppressWarnings("unused")
+    private void onEngineRestart() {
+        if (mPluginRegistry == null)
+            return;
+        mPluginRegistry.onEngineRestart();
+    }
+
     private static native long nativeAttach(FlutterNativeView view);
     private static native void nativeDestroy(long nativePlatformViewAndroid);
     private static native void nativeDetach(long nativePlatformViewAndroid);

shell/platform/android/platform_view_android.cc

@@ -157,6 +157,17 @@ void PlatformViewAndroid::HandlePlatformMessage(
   }
 }
 
+// |shell::PlatformView|
+void PlatformViewAndroid::OnEngineRestart() const {
+  JNIEnv* env = fml::jni::AttachCurrentThread();
+  fml::jni::ScopedJavaLocalRef<jobject> view = java_object_.get(env);
+  if (view.is_null()) {
+    // The Java object died.
+    return;
+  }
+  FlutterViewOnEngineRestart(fml::jni::AttachCurrentThread(), view.obj());
+}
+
 void PlatformViewAndroid::DispatchSemanticsAction(JNIEnv* env,
                                                   jint id,
                                                   jint action,