[android_webview] Use a fraction to calculate scroll offset.

android_webview/browser/in_process_view_renderer.h

Index: android_webview/browser/in_process_view_renderer.h
diff --git a/android_webview/browser/in_process_view_renderer.h b/android_webview/browser/in_process_view_renderer.h
index a864a39cea8576f3d1ff5d46c1c35948f256d2db..8594041511b53834c1b671bc97b9a45d0946ea42 100644
--- a/android_webview/browser/in_process_view_renderer.h
+++ b/android_webview/browser/in_process_view_renderer.h
@@ -79,6 +79,7 @@ class InProcessViewRenderer : public BrowserViewRenderer,
   virtual void DidDestroyCompositor(
       content::SynchronousCompositor* compositor) OVERRIDE;
   virtual void SetContinuousInvalidate(bool invalidate) OVERRIDE;
+  virtual void SetMaxRootLayerScrollOffset(gfx::Vector2dF new_value) OVERRIDE;
   virtual void SetTotalRootLayerScrollOffset(
       gfx::Vector2dF new_value_css) OVERRIDE;
   virtual void DidUpdateContent() OVERRIDE;
@@ -111,6 +112,8 @@ class InProcessViewRenderer : public BrowserViewRenderer,
 
   bool InitializeHwDraw();
 
+  gfx::Vector2d max_scroll_offset() const;
+
   // For debug tracing or logging. Return the string representation of this
   // view renderer's state and the |draw_info| if provided.
   std::string ToString(AwDrawGLInfo* draw_info) const;
@@ -160,7 +163,10 @@ class InProcessViewRenderer : public BrowserViewRenderer,
   gfx::Vector2d scroll_at_start_of_frame_;
 
   // Current scroll offset in CSS pixels.
-  gfx::Vector2dF scroll_offset_css_;
+  gfx::Vector2dF scroll_offset_dip_;
+
+  // Max scroll offset in CSS pixels.
+  gfx::Vector2dF max_scroll_offset_dip_;
 
   // Used to prevent rounding errors from accumulating enough to generate
   // visible skew (especially noticeable when scrolling up and down in the same