Synchronize OffscreenCanvas content with the placeholder canvas

third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h

Index: third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
diff --git a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
index eb015b8570b2f6222ba2bdad98516f0d2b89f713..e43b2c29730a7c42d38adf7487d475f9488361e0 100644
--- a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
+++ b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
@@ -26,6 +26,7 @@ class PLATFORM_EXPORT OffscreenCanvasFrameDispatcherImpl final
                                      uint32_t localId,
                                      uint64_t nonceHigh,
                                      uint64_t nonceLow,
+                                     int canvasId,
                                      int width,
                                      int height);
 
@@ -34,6 +35,7 @@ class PLATFORM_EXPORT OffscreenCanvasFrameDispatcherImpl final
   void dispatchFrame(RefPtr<StaticBitmapImage>,
                      double commitStartTime,
                      bool isWebGLSoftwareRendering = false) override;
+  void reclaimResource(unsigned resourceId) override;
 
   // cc::mojom::blink::MojoCompositorFrameSinkClient implementation.
   void DidReceiveCompositorFrameAck() override;
@@ -58,12 +60,15 @@ class PLATFORM_EXPORT OffscreenCanvasFrameDispatcherImpl final
   HashMap<unsigned, RefPtr<StaticBitmapImage>> m_cachedImages;
   HashMap<unsigned, std::unique_ptr<cc::SharedBitmap>> m_sharedBitmaps;
   HashMap<unsigned, GLuint> m_cachedTextureIds;
+  HashSet<unsigned> m_spareResourceLocks;
 
   bool verifyImageSize(const IntSize);
 
   cc::mojom::blink::MojoCompositorFrameSinkPtr m_sink;
   mojo::Binding<cc::mojom::blink::MojoCompositorFrameSinkClient> m_binding;
 
+  int m_placeholderCanvasId;
+
   void setTransferableResourceToSharedBitmap(cc::TransferableResource&,
                                              RefPtr<StaticBitmapImage>);
   void setTransferableResourceToSharedGPUContext(cc::TransferableResource&,