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

cc/scrollbar_layer_impl.h

Index: cc/scrollbar_layer_impl.h
diff --git a/cc/scrollbar_layer_impl.h b/cc/scrollbar_layer_impl.h
index f37dd050ce855026fa1f832d84b5b545ef792688..749917cc4bca04cea4c7da97d1652c90d061475b 100644
--- a/cc/scrollbar_layer_impl.h
+++ b/cc/scrollbar_layer_impl.h
@@ -31,6 +31,8 @@ public:
     void setForeTrackResourceId(ResourceProvider::ResourceId id) { m_foreTrackResourceId = id; }
     void setThumbResourceId(ResourceProvider::ResourceId id) { m_thumbResourceId = id; }
 
+    void setIsPinchZoomScrollbar(bool isPinchZoomScrollbar) { m_isPinchZoomScrollbar = isPinchZoomScrollbar; }
+    bool isPinchZoomScrollbar() { return m_isPinchZoomScrollbar; }
 
     // ScrollbarLayerImplBase implementation.
     virtual float currentPos() const OVERRIDE;
@@ -114,6 +116,7 @@ private:
     bool m_enabled;
     bool m_isCustomScrollbar;
     bool m_isOverlayScrollbar;
+    bool m_isPinchZoomScrollbar;
 };
 
 }