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;
+    virtual bool prepareMailbox(WebExternalTextureMailbox*, WebExternalBitmap *output_bitmap = 0) = 0;

[jamesr, 2013/07/03 21:53:02]

* goes with the type, not the parameter name. this parameter name isn't too
useful so blink style says you should omit it.

please update the comments for prepareMailbox() to say what happens if the
second parameter isn't null

 
     // 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