Allow WebExternalTextureLayerClient to work with mailboxes.

cc/texture_layer_client.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TEXTURE_LAYER_CLIENT_H_
 #define CC_TEXTURE_LAYER_CLIENT_H_
 
 namespace WebKit {
 class WebGraphicsContext3D;
 }
 
 namespace cc {
 class ResourceUpdateQueue;
+class TextureMailbox;
 
 class TextureLayerClient {
 public:
     // Called to prepare this layer's texture for compositing. The client may queue a texture
     // upload or copy on the ResourceUpdateQueue.
     // Returns the texture ID to be used for compositing.
     virtual unsigned prepareTexture(ResourceUpdateQueue&) = 0;
 
     // Returns the context that is providing the texture. Used for rate limiting and detecting lost context.
     virtual WebKit::WebGraphicsContext3D* context() = 0;
 
+    virtual bool prepareTextureMailbox(TextureMailbox*) = 0;

[piman, 2013/03/14 19:54:58]

Definitely worth a comment. In particular the meaning of the return value (false
== reuse existing).

+
 protected:
     virtual ~TextureLayerClient() { }
 };
 
 }
 
 #endif  // CC_TEXTURE_LAYER_CLIENT_H_