Pass accurate contentsScale to LayerImpl.

cc/scrollbar_layer_impl.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 CCScrollbarLayerImpl_h
 #define CCScrollbarLayerImpl_h
 
 #include "cc/layer_impl.h"
 #include "cc/scrollbar_geometry_fixed_thumb.h"
 #include <public/WebRect.h>
@@ skipping 59 matching lines @@
         virtual WebScrollbar::Orientation orientation() const;
         virtual bool isCustomScrollbar() const;
 
     private:
         ScrollbarLayerImpl* m_owner;
 
     };
 
     virtual const char* layerTypeAsString() const OVERRIDE;
 
+    IntRect scrollbarLayerRectToContentRect(const WebKit::WebRect& layerRect) const;
+
     Scrollbar m_scrollbar;
 
     ResourceProvider::ResourceId m_backTrackResourceId;
     ResourceProvider::ResourceId m_foreTrackResourceId;
     ResourceProvider::ResourceId m_thumbResourceId;
 
     scoped_ptr<ScrollbarGeometryFixedThumb> m_geometry;
 
     // Data to implement Scrollbar
     WebKit::WebScrollbar::ScrollbarOverlayStyle m_scrollbarOverlayStyle;
     WebKit::WebVector<WebKit::WebRect> m_tickmarks;
     WebKit::WebScrollbar::Orientation m_orientation;
     WebKit::WebScrollbar::ScrollbarControlSize m_controlSize;
     WebKit::WebScrollbar::ScrollbarPart m_pressedPart;
     WebKit::WebScrollbar::ScrollbarPart m_hoveredPart;
 
     float m_currentPos;
     int m_totalSize;
     int m_maximum;
 
     bool m_isScrollableAreaActive;
     bool m_isScrollViewScrollbar;
     bool m_enabled;
     bool m_isCustomScrollbar;
     bool m_isOverlayScrollbar;
 };
 
 }
 #endif