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

Source/WebCore/platform/graphics/chromium/DrawingBufferChromium.cpp

 /*
  * Copyright (c) 2010, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 185 matching lines @@
             updater.appendCopy(m_drawingBuffer->colorBuffer(), textureId, m_drawingBuffer->size());
 
         return textureId;
     }
 
     virtual WebKit::WebGraphicsContext3D* context() OVERRIDE
     {
         return GraphicsContext3DPrivate::extractWebGraphicsContext3D(m_drawingBuffer->graphicsContext3D());
     }
 
+    virtual bool prepareMailbox(WebKit::WebExternalTextureMailbox*) OVERRIDE { return false; }
+    virtual void mailboxReleased(const WebKit::WebExternalTextureMailbox&) OVERRIDE { }
+
     void clearTextureId()
     {
         m_layer->setTextureId(0);
     }
 
     WebKit::WebLayer* layer() { return m_layer->layer(); }
 
 private:
     DrawingBuffer* m_drawingBuffer;
     OwnPtr<WebKit::WebExternalTextureLayer> m_layer;
@@ skipping 38 matching lines @@
 void DrawingBuffer::clearPlatformLayer()
 {
     if (m_private)
         m_private->clearTextureId();
 
     m_context->flush();
 }
 #endif
 
 }