Disable overlay scrollbars in Blink when hidden by the compositor.

cc/layers/layer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1593 matching lines @@
   SetNeedsPushProperties();
 }
 
 void Layer::SetMayContainVideo(bool yes) {
   if (may_contain_video_ == yes)
     return;
   may_contain_video_ = yes;
   SetNeedsPushProperties();
 }
 
+void Layer::SetScrollbarsHiddenFromImplSide(bool hidden) {
+  if (inputs_.client)
+    inputs_.client->didChangeScrollbarsHidden(hidden);
+}
+
 bool Layer::FilterIsAnimating() const {
   return GetAnimationHost()->IsAnimatingFilterProperty(
       element_id(), GetElementTypeForAnimation());
 }
 
 bool Layer::TransformIsAnimating() const {
   return GetAnimationHost()->IsAnimatingTransformProperty(
       element_id(), GetElementTypeForAnimation());
 }
 
@@ skipping 265 matching lines @@
 
 LayerTree* Layer::GetLayerTree() const {
   return layer_tree_;
 }
 
 void Layer::SetLayerIdForTesting(int id) {
   inputs_.layer_id = id;
 }
 
 }  // namespace cc