cc: add layer usage hint to texture layer

cc/texture_layer.h

 // Copyright 2010 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_H_
 #define CC_TEXTURE_LAYER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "cc/cc_export.h"
 #include "cc/layer.h"
 #include "cc/texture_mailbox.h"
 
 namespace WebKit { class WebGraphicsContext3D; }
 
 namespace cc {
 
 class TextureLayerClient;
 
 // A Layer containing a the rendered output of a plugin instance.
 class CC_EXPORT TextureLayer : public Layer {
  public:
   // If this texture layer requires special preparation logic for each frame
   // driven by the compositor, pass in a non-nil client. Pass in a nil client
   // pointer if texture updates are driven by an external process.
-  static scoped_refptr<TextureLayer> Create(TextureLayerClient* client);
+  static scoped_refptr<TextureLayer> Create(TextureLayerClient* client, bool single_buffer = false);
 
   // Used when mailbox names are specified instead of texture IDs.
   static scoped_refptr<TextureLayer> CreateForMailbox();
 
   void ClearClient() { client_ = NULL; }
 
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
 
   // Sets whether this texture should be Y-flipped at draw time. Defaults to
@@ skipping 33 matching lines @@
   virtual bool DrawsContent() const OVERRIDE;
   virtual void Update(ResourceUpdateQueue* queue,
                       const OcclusionTracker* occlusion,
                       RenderingStats* stats) OVERRIDE;
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
   virtual bool BlocksPendingCommit() const OVERRIDE;
 
   virtual bool CanClipSelf() const OVERRIDE;
 
  protected:
-  TextureLayer(TextureLayerClient* client, bool uses_mailbox);
+  TextureLayer(TextureLayerClient* client, bool uses_mailbox, bool single_buffer);
   virtual ~TextureLayer();
 
  private:
   TextureLayerClient* client_;
   bool uses_mailbox_;
 
   bool flipped_;
   gfx::PointF uv_top_left_;
   gfx::PointF uv_bottom_right_;
   // [bottom left, top left, top right, bottom right]
   float vertex_opacity_[4];
   bool premultiplied_alpha_;
   bool rate_limit_context_;
   bool context_lost_;
   bool content_committed_;
 
   unsigned texture_id_;
   TextureMailbox texture_mailbox_;
   bool own_mailbox_;
 
+  // indicate the layer usage, it's a const after set in constructor
+  bool single_buffer_;
+
   DISALLOW_COPY_AND_ASSIGN(TextureLayer);
 };
 
 }
 #endif  // CC_TEXTURE_LAYER_H_