Impl thread smooth scrolling.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index fe9afc219e6dd30caa9cd94e0c1a3d78f67cf0f2..e5412bbe005b09b1a1c75f0811b834d60204e5f6 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -126,6 +126,9 @@ class CC_EXPORT LayerTreeHostImpl
   virtual InputHandler::ScrollStatus ScrollBegin(
       const gfx::Point& viewport_point,
       InputHandler::ScrollInputType type) OVERRIDE;
+  virtual InputHandler::ScrollStatus ScrollAnimated(
+      const gfx::Point& viewport_point,
+      const gfx::Vector2dF& scroll_delta) OVERRIDE;
   virtual bool ScrollBy(const gfx::Point& viewport_point,
                         const gfx::Vector2dF& scroll_delta) OVERRIDE;
   virtual bool ScrollVerticallyByPage(const gfx::Point& viewport_point,
@@ -552,6 +555,14 @@ class CC_EXPORT LayerTreeHostImpl
 
   void NotifySwapPromiseMonitorsOfSetNeedsRedraw();
 
+  class IsScrollOffsetAnimationFinished {
+   public:
+    bool operator()(const AnimationEvent& event) const {
+      return event.type == AnimationEvent::Finished &&
+             event.target_property == Animation::ScrollOffset;
+    }
+  };
+
   typedef base::hash_map<UIResourceId, UIResourceData>
       UIResourceMap;
   UIResourceMap ui_resource_map_;