Implement desktop compatibility viewport

cc/layer_tree_host_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_LAYER_TREE_HOST_CLIENT_H_
 #define CC_LAYER_TREE_HOST_CLIENT_H_
 
 #include "base/memory/scoped_ptr.h"
 
 namespace gfx {
 class Vector2d;
 }
 
 namespace cc {
 class FontAtlas;
 class InputHandler;
 class OutputSurface;
 
 class LayerTreeHostClient {
 public:
     virtual void willBeginFrame() = 0;
     // Marks finishing compositing-related tasks on the main thread. In threaded mode, this corresponds to didCommit().
     virtual void didBeginFrame() = 0;
     virtual void animate(double frameBeginTime) = 0;
     virtual void layout() = 0;
-    virtual void applyScrollAndScale(gfx::Vector2d scrollDelta, float pageScale) = 0;
+    virtual void applyScrollAndScale(gfx::Vector2d scrollDelta, float pageScale, gfx::Vector2d desktopCompatibilityViewportOffsetFromScrollPositionDelta) = 0;
     virtual scoped_ptr<OutputSurface> createOutputSurface() = 0;
     virtual void didRecreateOutputSurface(bool success) = 0;
     virtual scoped_ptr<InputHandler> createInputHandler() = 0;
     virtual void willCommit() = 0;
     virtual void didCommit() = 0;
     virtual void didCommitAndDrawFrame() = 0;
     virtual void didCompleteSwapBuffers() = 0;
 
     // Used only in the single-threaded path.
     virtual void scheduleComposite() = 0;
 
     // Creates a font atlas to use for debug visualizations.
     virtual scoped_ptr<FontAtlas> createFontAtlas() = 0;
 
 protected:
     virtual ~LayerTreeHostClient() { }
 };
 
 }
 
 #endif  // CC_LAYER_TREE_HOST_CLIENT_H_