Don't fade in overlay scrollbar when user interacting the content under scrollbar.

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 150bbccb5070bcf60a176c99b155fd3e4d6b783d..d1876f91772a6316227b29520cf52e3e9c2ef0cb 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3487,7 +3487,8 @@ void LayerTreeHostImpl::MouseUp() {
   }
 }
 
-void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point) {
+void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point,
+                                    bool is_mouse_down) {
   gfx::PointF device_viewport_point = gfx::ScalePoint(
       gfx::PointF(viewport_point), active_tree_->device_scale_factor());
   LayerImpl* layer_impl =
@@ -3530,7 +3531,7 @@ void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point) {
   if (!new_animation_controller)
     return;
 
-  new_animation_controller->DidMouseMove(device_viewport_point);
+  new_animation_controller->DidMouseMove(device_viewport_point, is_mouse_down);
 }
 
 void LayerTreeHostImpl::MouseLeave() {