Support high DPI scrollbar on top level web frame.

cc/ScrollbarLayerChromium.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 ScrollbarLayerChromium_h
 #define ScrollbarLayerChromium_h
 
 #if USE(ACCELERATED_COMPOSITING)
 
 #include "LayerChromium.h"
 #include "LayerTextureUpdater.h"
 #include <public/WebScrollbar.h>
 #include <public/WebScrollbarThemeGeometry.h>
 #include <public/WebScrollbarThemePainter.h>
 
 namespace cc {
 
 class Scrollbar;
 class ScrollbarThemeComposite;
 class CCTextureUpdateQueue;
 
 class ScrollbarLayerChromium : public LayerChromium {
 public:
     virtual PassOwnPtr<CCLayerImpl> createCCLayerImpl() OVERRIDE;
     static PassRefPtr<ScrollbarLayerChromium> create(PassOwnPtr<WebKit::WebScrollbar>, WebKit::WebScrollbarThemePainter, PassOwnPtr<WebKit::WebScrollbarThemeGeometry>, int scrollLayerId);
 
     // LayerChromium interface
+    virtual bool needsContentsScale() const OVERRIDE;
+    virtual IntSize contentBounds() const OVERRIDE;
     virtual void setTexturePriorities(const CCPriorityCalculator&) OVERRIDE;
     virtual void update(CCTextureUpdateQueue&, const CCOcclusionTracker*, CCRenderingStats&) OVERRIDE;
     virtual void setLayerTreeHost(CCLayerTreeHost*) OVERRIDE;
     virtual void pushPropertiesTo(CCLayerImpl*) OVERRIDE;
 
     int scrollLayerId() const { return m_scrollLayerId; }
     void setScrollLayerId(int id) { m_scrollLayerId = id; }
 
     virtual ScrollbarLayerChromium* toScrollbarLayerChromium() OVERRIDE { return this; }
 
@@ skipping 18 matching lines @@
     // All the parts of the scrollbar except the thumb
     OwnPtr<LayerTextureUpdater::Texture> m_backTrack;
     OwnPtr<LayerTextureUpdater::Texture> m_foreTrack;
     OwnPtr<LayerTextureUpdater::Texture> m_thumb;
 };
 
 }
 #endif // USE(ACCELERATED_COMPOSITING)
 
 #endif