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

cc/layer_tree_impl.h

Index: cc/layer_tree_impl.h
diff --git a/cc/layer_tree_impl.h b/cc/layer_tree_impl.h
index 1b80c2a60c7d70eaa0ef0c35f8a02d06c6c1d4cd..54a1214ed47c06742e391ddc1920234b2574d30d 100644
--- a/cc/layer_tree_impl.h
+++ b/cc/layer_tree_impl.h
@@ -34,6 +34,7 @@ class OutputSurface;
 class PaintTimeCounter;
 class Proxy;
 class ResourceProvider;
+class ScrollbarLayerImpl;
 class TileManager;
 struct RendererCapabilities;
 
@@ -191,11 +192,26 @@ class CC_EXPORT LayerTreeImpl {
   // Useful for debug assertions, probably shouldn't be used for anything else.
   Proxy* proxy() const;
 
+  void SetPinchZoomHorizontalLayerId(int layer_id);
+  void SetPinchZoomVerticalLayerId(int layer_id);
+
+  void DidBeginScroll();
+  void DidUpdateScroll();
+  void DidEndScroll();
+
 protected:
   LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl);
 
   void UpdateSolidColorScrollbars();
 
+  // Hide existence of pinch-zoom scrollbars.
+  void UpdatePinchZoomScrollbars();
+  void FadeInPinchZoomScrollbars();
+  void FadeOutPinchZoomScrollbars();
+  ScrollbarLayerImpl* PinchZoomScrollbarHorizontal();
+  ScrollbarLayerImpl* PinchZoomScrollbarVertical();
+  bool HasPinchZoomScrollbars() const;
+
   LayerTreeHostImpl* layer_tree_host_impl_;
   int source_frame_number_;
   scoped_ptr<LayerImpl> root_layer_;
@@ -205,6 +221,9 @@ protected:
   SkColor background_color_;
   bool has_transparent_background_;
 
+  int pinch_zoom_scrollbar_horizontal_layer_id_;
+  int pinch_zoom_scrollbar_vertical_layer_id_;
+
   float page_scale_factor_;
   float page_scale_delta_;
   float sent_page_scale_delta_;