Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/scrollbar_layer.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_SCROLLBAR_LAYER_H_
 #define CC_SCROLLBAR_LAYER_H_
 
 #include "cc/cc_export.h"
 #include "cc/contents_scaling_layer.h"
@@ skipping 15 matching lines @@
     static scoped_refptr<ScrollbarLayer> create(
         scoped_ptr<WebKit::WebScrollbar>,
         scoped_ptr<ScrollbarThemePainter>,
         scoped_ptr<WebKit::WebScrollbarThemeGeometry>,
         int scrollLayerId);
 
     int scrollLayerId() const { return m_scrollLayerId; }
     void setScrollLayerId(int id);
 
     WebKit::WebScrollbar::Orientation orientation() const;
+    bool isOverlay() const;
 
     // Layer interface
     virtual void setTexturePriorities(const PriorityCalculator&) OVERRIDE;
     virtual void update(ResourceUpdateQueue&, const OcclusionTracker*, RenderingStats*) OVERRIDE;
     virtual void setLayerTreeHost(LayerTreeHost*) OVERRIDE;
     virtual void pushPropertiesTo(LayerImpl*) OVERRIDE;
     virtual void calculateContentsScale(
         float idealContentsScale,
         bool animatingTransformToScreen,
         float* contentsScaleX,
@@ skipping 35 matching lines @@
     scoped_refptr<CachingBitmapContentLayerUpdater> m_thumbUpdater;
 
     // All the parts of the scrollbar except the thumb
     scoped_ptr<LayerUpdater::Resource> m_backTrack;
     scoped_ptr<LayerUpdater::Resource> m_foreTrack;
     scoped_ptr<LayerUpdater::Resource> m_thumb;
 };
 
 }
 #endif  // CC_SCROLLBAR_LAYER_H_