Delegate root layer scroll offset to android_webview.

content/public/browser/android/synchronous_compositor.h

 // Copyright 2013 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 CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_
 #define CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_
 
 #include "ui/gfx/rect.h"
 #include "ui/gfx/size.h"
 
@@ skipping 33 matching lines @@
   // and clip set there-in).
   virtual bool DemandDrawSw(SkCanvas* canvas) = 0;
 
   // "On demand" hardware draw. The content is first clipped to |damage_area|,
   // then transformed through |transform|, and finally clipped to |view_size|.
   virtual bool DemandDrawHw(
       gfx::Size view_size,
       const gfx::Transform& transform,
       gfx::Rect damage_area) = 0;
 
+  // Should be called by the embedder after the embedder had modified the
+  // scroll offset of the root layer (as returned by
+  // SynchronousCompositorClient::GetTotalRootLayerScrollOffset).
+  virtual void DidChangeRootLayerScrollOffset() = 0;
+
  protected:
   virtual ~SynchronousCompositor() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_