Blink API to allow mailbox usage with texture layers for WebGL and Canvas2D.

Source/WebCore/platform/graphics/chromium/Canvas2DLayerBridge.h

 /*
  * Copyright (C) 2012 Google 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 41 matching lines @@
     static PassOwnPtr<Canvas2DLayerBridge> create(PassRefPtr<GraphicsContext3D> context, const IntSize& size, ThreadMode threading, unsigned textureId)
     {
         return adoptPtr(new Canvas2DLayerBridge(context, size, threading, textureId));
     }
 
     virtual ~Canvas2DLayerBridge();
 
     // WebKit::WebExternalTextureLayerClient implementation.
     virtual unsigned prepareTexture(WebKit::WebTextureUpdater&) OVERRIDE;
     virtual WebKit::WebGraphicsContext3D* context() OVERRIDE;
+    virtual bool prepareMailbox(WebKit::WebExternalTextureMailbox*) OVERRIDE { return false; }
+    virtual void mailboxReleased(const WebKit::WebExternalTextureMailbox&) OVERRIDE { }
 
     // SkDeferredCanvas::NotificationClient implementation
     virtual void prepareForDraw() OVERRIDE;
     virtual void storageAllocatedForRecordingChanged(size_t) OVERRIDE;
     virtual void flushedDrawCommands() OVERRIDE;
     virtual void skippedPendingDrawCommands() OVERRIDE;
 
     // Methods used by Canvas2DLayerManager
     virtual size_t freeMemoryIfPossible(size_t); // virtual for mocking
     virtual void flush(); // virtual for mocking
@@ skipping 20 matching lines @@
     int m_framesPending;
 
     friend class WTF::DoublyLinkedListNode<Canvas2DLayerBridge>;
     Canvas2DLayerBridge* m_next;
     Canvas2DLayerBridge* m_prev;
 };
 
 }
 
 #endif