Allow DrawingBuffer to present to a bitmap.

public/platform/WebExternalTextureLayerClient.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 14 matching lines @@
 
 #ifndef WebExternalTextureLayerClient_h
 #define WebExternalTextureLayerClient_h
 
 #include "WebCommon.h"
 #include "WebSize.h"
 
 namespace WebKit {
 
 class WebGraphicsContext3D;
+class WebExternalBitmap;
 struct WebExternalTextureMailbox;
 
 class WebTextureUpdater {
 public:
     virtual void appendCopy(unsigned sourceTexture, unsigned destinationTexture, WebSize) = 0;
 
 protected:
     virtual ~WebTextureUpdater() { }
 };
 
 class WebExternalTextureLayerClient {
 public:
     virtual unsigned prepareTexture(WebTextureUpdater&) = 0;
     virtual WebGraphicsContext3D* context() = 0;
 
-    // Returns true and provides a mailbox if a new frame is available.
-    // Returns false if no new data is available and the old mailbox is to be reused.
-    virtual bool prepareMailbox(WebExternalTextureMailbox*) = 0;
+    // Returns true and provides a mailbox if a new frame is available. If the WebExternalBitmap
+    // isn't 0, then it should also be filled in with the contents of this frame.
+    // Returns false if no new data is available and the old mailbox and bitmap are to be reused.
+    virtual bool prepareMailbox(WebExternalTextureMailbox*, WebExternalBitmap* = 0) = 0;
 
     // Notifies the client when a mailbox is no longer in use by the compositor and provides
     // a sync point to wait on before the mailbox could be consumes again by the client.
     virtual void mailboxReleased(const WebExternalTextureMailbox&) = 0;
 
 protected:
     virtual ~WebExternalTextureLayerClient() { }
 };
 
 } // namespace WebKit
 
 #endif // WebExternalTextureLayerClient_h