Add the ability to dispose host objects

Some host objects hold on to a lot of state and take time to tear down. This
patch adds the ability to dispose them eagerly to release resources faster.

sky/engine/core/compositing/Scene.cpp

@@ -25,6 +25,10 @@ Scene::Scene(std::unique_ptr<sky::compositor::Layer> rootLayer,
 
 Scene::~Scene() {}
 
+void Scene::dispose() {
+  ClearDartWrapper();
+}
+
 std::unique_ptr<sky::compositor::LayerTree> Scene::takeLayerTree() {
   return std::move(m_layerTree);
 }

sky/engine/core/compositing/Scene.h

@@ -28,6 +28,8 @@ class Scene : public RefCounted<Scene>, public DartWrappable {
 
   std::unique_ptr<sky::compositor::LayerTree> takeLayerTree();
 
+  void dispose();
+
  private:
   explicit Scene(std::unique_ptr<sky::compositor::Layer> rootLayer,
                  uint32_t rasterizerTracingThreshold);

sky/engine/core/compositing/Scene.idl

@@ -4,4 +4,5 @@
 
 // An opaque handle to a composited scene.
 interface Scene {
+    void dispose();
 };

sky/engine/core/compositing/SceneBuilder.cpp

@@ -131,7 +131,9 @@ PassRefPtr<Scene> SceneBuilder::build()
     m_currentLayer = nullptr;
     int32_t threshold = m_currentRasterizerTracingThreshold;
     m_currentRasterizerTracingThreshold = 0;
-    return Scene::create(std::move(m_rootLayer), threshold);
+    RefPtr<Scene> scene = Scene::create(std::move(m_rootLayer), threshold);
+    ClearDartWrapper();
+    return scene.release();
 }
 
 } // namespace blink

sky/engine/core/painting/CanvasImage.cpp

@@ -20,4 +20,8 @@ int CanvasImage::height() const {
   return image_->height();
 }
 
+void CanvasImage::dispose() {
+  ClearDartWrapper();
+}
+
 }  // namespace blink

sky/engine/core/painting/CanvasImage.h

@@ -20,6 +20,7 @@ class CanvasImage final : public RefCounted<CanvasImage>,
 
   int width() const;
   int height() const;
+  void dispose();
 
   SkImage* image() const { return image_.get(); }
   void setImage(PassRefPtr<SkImage> image) { image_ = image; }

sky/engine/core/painting/Image.idl

@@ -9,4 +9,6 @@
     // TODO(ianh): convert this to a Size
     readonly attribute long width;  // width in number of image pixels
     readonly attribute long height; // height in number of image pixels
+
+    void dispose();
 };

sky/engine/core/painting/Picture.cpp

@@ -28,4 +28,9 @@ void Picture::playback(Canvas* canvas)
     m_picture->playback(canvas->skCanvas());
 }
 
+void Picture::dispose()
+{
+    ClearDartWrapper();
+}
+
 } // namespace blink

sky/engine/core/painting/Picture.h

@@ -23,6 +23,7 @@ public:
     SkPicture* toSkia() const { return m_picture.get(); }
 
     void playback(Canvas* canvas);
+    void dispose();
 
 private:
     explicit Picture(PassRefPtr<SkPicture> skPicture);

sky/engine/core/painting/Picture.idl

@@ -7,4 +7,6 @@ interface Picture {
   // canvas. Using the Canvas drawPicture entry point gives the destination
   // canvas the option of just taking a ref.
   void playback(Canvas canvas);
+
+  void dispose();
 };

sky/engine/core/painting/PictureRecorder.cpp

@@ -34,7 +34,9 @@ PassRefPtr<Picture> PictureRecorder::endRecording()
     RefPtr<Picture> picture = Picture::create(
         adoptRef(m_pictureRecorder.endRecording()));
     m_canvas->clearSkCanvas();
+    m_canvas->ClearDartWrapper();
     m_canvas = nullptr;
+    ClearDartWrapper();
     return picture.release();
 }
 
@@ -45,7 +47,9 @@ PassRefPtr<Drawable> PictureRecorder::endRecordingAsDrawable()
     RefPtr<Drawable> drawable = Drawable::create(
         adoptRef(m_pictureRecorder.endRecordingAsDrawable()));
     m_canvas->clearSkCanvas();
+    m_canvas->ClearDartWrapper();
     m_canvas = nullptr;
+    ClearDartWrapper();
     return drawable.release();
 }
 

sky/engine/core/painting/PictureRecorder.idl

@@ -4,7 +4,6 @@
 [
   Constructor()
 ] interface PictureRecorder {
-  readonly attribute boolean isRecording;
   Picture endRecording();
   Drawable endRecordingAsDrawable();
 };

sky/engine/tonic/dart_wrappable.cc

@@ -63,6 +63,16 @@ void DartWrappable::AssociateWithDartWrapper(Dart_NativeArguments args) {
       wrapper, this, info.size_in_bytes, &FinalizeDartWrapper);
 }
 
+void DartWrappable::ClearDartWrapper() {
+  DCHECK(dart_wrapper_);
+  Dart_Handle wrapper = Dart_HandleFromWeakPersistent(dart_wrapper_);
+  CHECK(!LogIfError(Dart_SetNativeInstanceField(wrapper, kPeerIndex, 0)));
+  CHECK(!LogIfError(Dart_SetNativeInstanceField(wrapper, kWrapperInfoIndex, 0)));
+  Dart_DeleteWeakPersistentHandle(Dart_CurrentIsolate(), dart_wrapper_);
+  dart_wrapper_ = nullptr;
+  GetDartWrapperInfo().deref_object(this);
+}
+
 void DartWrappable::FinalizeDartWrapper(void* isolate_callback_data,
                                         Dart_WeakPersistentHandle wrapper,
                                         void* peer) {

sky/engine/tonic/dart_wrappable.h

@@ -41,6 +41,7 @@ class DartWrappable {
 
   Dart_Handle CreateDartWrapper(DartState* dart_state);
   void AssociateWithDartWrapper(Dart_NativeArguments args);
+  void ClearDartWrapper(); // Warning: Might delete this.
   Dart_WeakPersistentHandle dart_wrapper() const { return dart_wrapper_; }
 
  protected:

sky/shell/ui/engine.cc

@@ -13,15 +13,15 @@
 #include "mojo/data_pipe_utils/data_pipe_utils.h"
 #include "mojo/public/cpp/application/connect.h"
 #include "services/asset_bundle/asset_unpacker_job.h"
-#include "sky/engine/public/platform/WebInputEvent.h"
-#include "sky/engine/public/platform/sky_display_metrics.h"
 #include "sky/engine/public/platform/sky_display_metrics.h"
+#include "sky/engine/public/platform/WebInputEvent.h"
 #include "sky/engine/public/web/Sky.h"
 #include "sky/engine/public/web/WebRuntimeFeatures.h"
 #include "sky/shell/dart/dart_library_provider_files.h"
 #include "sky/shell/dart/dart_library_provider_network.h"
 #include "sky/shell/service_provider.h"
 #include "sky/shell/switches.h"
+#include "sky/shell/switches.h"
 #include "sky/shell/ui/animator.h"
 #include "sky/shell/ui/internals.h"
 #include "sky/shell/ui/platform_impl.h"