cancel overlay-scrollbar hover state when moving pointer out of window for ChromeOS

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 ccbd9e7393ee42373e8fea65dfebf6b39727e481..020e9ee7530d6e7e4a90e7f6b232cd5eba79a6d8 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -180,6 +180,7 @@ class CC_EXPORT LayerTreeHostImpl
   void MouseDown() override;
   void MouseUp() override;
   void MouseMoveAt(const gfx::Point& viewport_point) override;
+  void MouseLeave() override;
 
   void PinchGestureBegin() override;
   void PinchGestureUpdate(float magnify_delta,
@@ -746,6 +747,7 @@ class CC_EXPORT LayerTreeHostImpl
   bool wheel_scrolling_;
   bool scroll_affects_scroll_handler_;
   int scroll_layer_id_when_mouse_over_scrollbar_;
+  int scroll_layer_id_when_mouse_near_scrollbar_;

[aelias_OOO_until_Jul13, 2016/10/07 16:26:19]

Why's this state needed?  Can't you just loop through *all* scrollbar animators
and call DidMouseMoveOffScrollbar on them instead?

To avoid unnecessary work, I suggest making DidMouseMoveOffScrollbar avoid
calling StartAnimation() if nothing changed.

[chaopeng, 2016/10/07 18:06:16]

loop through *all* scrollbar animators is better idea. CL updated, PTAL. Thank
you.

   int captured_scrollbar_layer_id_;
 
   std::vector<std::unique_ptr<SwapPromise>>