Synchronize OffscreenCanvas content with the placeholder canvas

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

 /*
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.  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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 66 matching lines @@
   // the current frame. Since this may initiate a deferred image
   // decoding, PreCacheMetadata requires a InspectorPaintImageEvent
   // during call.
   enum MetadataMode { UseCurrentMetadata, PreCacheMetadata };
   virtual bool currentFrameKnownToBeOpaque(
       MetadataMode = UseCurrentMetadata) = 0;
 
   virtual bool currentFrameIsComplete() { return false; }
   virtual bool currentFrameIsLazyDecoded() { return false; }
   virtual bool isTextureBacked();
+  virtual void transfer() {}

[xidachen, 2016/11/14 19:05:03]

I am not sure why this function is moved from StaticBitmapImage to Image. The
StaticBitmapImage should be the only class that is transferable.

 
   // Derived classes should override this if they can assure that the current
   // image frame contains only resources from its own security origin.
   virtual bool currentFrameHasSingleSecurityOrigin() const { return false; }
 
   static Image* nullImage();
   bool isNull() const { return size().isEmpty(); }
 
   virtual bool usesContainerSize() const { return false; }
   virtual bool hasRelativeSize() const { return false; }
@@ skipping 122 matching lines @@
   bool m_imageObserverDisabled;
 };
 
 #define DEFINE_IMAGE_TYPE_CASTS(typeName)                          \
   DEFINE_TYPE_CASTS(typeName, Image, image, image->is##typeName(), \
                     image.is##typeName())
 
 }  // namespace blink
 
 #endif