[android_webview] Use a fraction to calculate scroll offset.

content/public/browser/android/synchronous_compositor_client.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_CLIENT_H_
 #define CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_CLIENT_H_
 
 #include "base/basictypes.h"
 #include "ui/gfx/vector2d_f.h"
 
 namespace content {
 
 class SynchronousCompositor;
 
 class SynchronousCompositorClient {
  public:
   // Indication to the client that |compositor| is now initialized on the
   // compositor thread, and open for business.
   virtual void DidInitializeCompositor(SynchronousCompositor* compositor) = 0;
 
   // Indication to the client that |compositor| is going out of scope, and
   // must not be accessed within or after this call.
   // NOTE if the client goes away before the compositor it must call
   // SynchronousCompositor::SetClient(NULL) to release the back pointer.
   virtual void DidDestroyCompositor(SynchronousCompositor* compositor) = 0;
 
   // See LayerScrollOffsetDelegate for details.
+  virtual void SetMaxRootLayerScrollOffset(gfx::Vector2dF new_value) = 0;
   virtual void SetTotalRootLayerScrollOffset(gfx::Vector2dF new_value) = 0;
   virtual gfx::Vector2dF GetTotalRootLayerScrollOffset() = 0;
   virtual void DidOverscroll(gfx::Vector2dF accumulated_overscroll,
                              gfx::Vector2dF latest_overscroll_delta,
                              gfx::Vector2dF current_fling_velocity) = 0;
 
   // When true, should periodically call
   // SynchronousCompositorOutputSurface::DemandDrawHw. Note that this value
   // can change inside DemandDrawHw call.
   virtual void SetContinuousInvalidate(bool invalidate) = 0;
 
   virtual void DidUpdateContent() = 0;
 
  protected:
   SynchronousCompositorClient() {}
   virtual ~SynchronousCompositorClient() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SynchronousCompositorClient);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_CLIENT_H_