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

cc/layer_tree_host.h

Index: cc/layer_tree_host.h
diff --git a/cc/layer_tree_host.h b/cc/layer_tree_host.h
index e5719ec353b3c58ef38b74ef17bf70935f1efe16..82e14f9607d2c83c5cdd2ecf1582747542a4bfaf 100644
--- a/cc/layer_tree_host.h
+++ b/cc/layer_tree_host.h
@@ -53,6 +53,7 @@ class PrioritizedResource;
 class Region;
 class ResourceProvider;
 class ResourceUpdateQueue;
+class ScrollbarLayer;
 class TopControlsManager;
 struct ScrollAndScaleSet;
 
@@ -96,6 +97,8 @@ public:
     void layout();
     void beginCommitOnImplThread(LayerTreeHostImpl*);
     void finishCommitOnImplThread(LayerTreeHostImpl*);
+    void setPinchZoomScrollbarsBoundsAndPosition();
+    void createAndAddPinchZoomScrollbars();
     void willCommit();
     void commitComplete();
     scoped_ptr<OutputSurface> createOutputSurface();
@@ -151,6 +154,8 @@ public:
     void setAnimationEvents(scoped_ptr<AnimationEventsVector>, base::Time wallClockTime);
 
     Layer* rootLayer() { return m_rootLayer.get(); }
+    const Layer* rootScrollLayer() const;
+
     const Layer* rootLayer() const { return m_rootLayer.get(); }
     void setRootLayer(scoped_refptr<Layer>);
 
@@ -253,6 +258,8 @@ private:
 
     scoped_refptr<Layer> m_rootLayer;
     scoped_refptr<HeadsUpDisplayLayer> m_hudLayer;
+    scoped_refptr<ScrollbarLayer> m_pinchZoomScrollbarHorizontal;
+    scoped_refptr<ScrollbarLayer> m_pinchZoomScrollbarVertical;
 
     scoped_ptr<PrioritizedResourceManager> m_contentsTextureManager;
     scoped_ptr<PrioritizedResource> m_surfaceMemoryPlaceholder;