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 5c1ce68d759f4fb174708b7ee6792bbce1209f50..7224cdf9a274511f0cbad853778c3a97f4a8998d 100644
--- a/cc/layer_tree_host.h
+++ b/cc/layer_tree_host.h
@@ -47,6 +47,7 @@ class LayerTreeHostImplClient;
 class PrioritizedResourceManager;
 class ResourceUpdateQueue;
 class HeadsUpDisplayLayer;
+class PinchZoomScrollbarLayer;
 class Region;
 struct ScrollAndScaleSet;
 
@@ -244,6 +245,8 @@ private:
 
     scoped_refptr<Layer> m_rootLayer;
     scoped_refptr<HeadsUpDisplayLayer> m_hudLayer;
+    scoped_refptr<PinchZoomScrollbarLayer> m_pinchZoomScrollbarVertical;
+    scoped_refptr<PinchZoomScrollbarLayer> m_pinchZoomScrollbarHorizontal;
 
     scoped_ptr<PrioritizedResourceManager> m_contentsTextureManager;
     scoped_ptr<PrioritizedResource> m_surfaceMemoryPlaceholder;