Pass MouseUp to the captured scrollbar animation controller in layer tree

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index ecf60cf97cc12578d03d7175fa08acc1dd916b00..e8e0fb350a08cd7c141945d200846c10139e3545 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3240,10 +3240,8 @@ void LayerTreeHostImpl::MouseDown() {
 }
 
 void LayerTreeHostImpl::MouseUp() {
-  ScrollbarAnimationController* animation_controller =
-      ScrollbarAnimationControllerForId(scroll_layer_id_mouse_currently_over_);
-  if (animation_controller)
-    animation_controller->DidMouseUp();
+  for (auto& pair : scrollbar_animation_controllers_)

[bokan, 2017/02/10 15:56:40]

This only needs to notify the one captured scrollbar_animation_controller. Lets
have MouseDown tell the LTHI (via ScrollbarAnimationControllerClient) when a
scrollbar controller is captured. Then MouseUp here can just call DidMouseUp on
the captured controller.

+    pair.second->DidMouseUp();
 }
 
 void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point) {