Synchronize OffscreenCanvas content with the placeholder canvas

third_party/WebKit/Source/core/html/HTMLCanvasElement.h

 /*
  * Copyright (C) 2004, 2006, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 28 matching lines @@
 #include "core/html/canvas/CanvasDrawListener.h"
 #include "core/html/canvas/CanvasImageSource.h"
 #include "core/imagebitmap/ImageBitmapSource.h"
 #include "core/page/PageVisibilityObserver.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/graphics/CanvasSurfaceLayerBridge.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/GraphicsTypes3D.h"
 #include "platform/graphics/ImageBufferClient.h"
+#include "platform/graphics/OffscreenCanvasPlaceholder.h"
 #include "platform/heap/Handle.h"
 #include <memory>
 
 #define CanvasDefaultInterpolationQuality InterpolationLow
 
 namespace blink {
 
 class AffineTransform;
 class CanvasContextCreationAttributes;
 class CanvasRenderingContext;
@@ skipping 11 matching lines @@
 class
     CanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContextOrImageBitmapRenderingContext;
 typedef CanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContextOrImageBitmapRenderingContext
     RenderingContext;
 
 class CORE_EXPORT HTMLCanvasElement final : public HTMLElement,
                                             public ContextLifecycleObserver,
                                             public PageVisibilityObserver,
                                             public CanvasImageSource,
                                             public ImageBufferClient,
-                                            public ImageBitmapSource {
+                                            public ImageBitmapSource,
+                                            public OffscreenCanvasPlaceholder {
   DEFINE_WRAPPERTYPEINFO();
   USING_GARBAGE_COLLECTED_MIXIN(HTMLCanvasElement);
   USING_PRE_FINALIZER(HTMLCanvasElement, dispose);
 
  public:
   using Node::getExecutionContext;
 
   DECLARE_NODE_FACTORY(HTMLCanvasElement);
   ~HTMLCanvasElement() override;
 
@@ skipping 211 matching lines @@
   // Used for OffscreenCanvas that controls this HTML canvas element
   std::unique_ptr<CanvasSurfaceLayerBridge> m_surfaceLayerBridge;
 
   int m_numFramesSinceLastRenderingModeSwitch;
   bool m_pendingRenderingModeSwitch;
 };
 
 }  // namespace blink
 
 #endif  // HTMLCanvasElement_h