Disable overlay scrollbars in Blink when hidden by the compositor.

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <stddef.h>
 
 #include <bitset>
@@ skipping 336 matching lines @@
       TreePriority tree_priority) override;
   void SetIsLikelyToRequireADraw(bool is_likely_to_require_a_draw) override;
   gfx::ColorSpace GetTileColorSpace() const override;
 
   // ScrollbarAnimationControllerClient implementation.
   void PostDelayedScrollbarAnimationTask(const base::Closure& task,
                                          base::TimeDelta delay) override;
   void SetNeedsAnimateForScrollbarAnimation() override;
   void SetNeedsRedrawForScrollbarAnimation() override;
   ScrollbarSet ScrollbarsFor(int scroll_layer_id) const override;
+  void DidChangeScrollbarVisibility() override;
 
   // VideoBeginFrameSource implementation.
   void AddVideoFrameController(VideoFrameController* controller) override;
   void RemoveVideoFrameController(VideoFrameController* controller) override;
 
   // CompositorFrameSinkClient implementation.
   void SetBeginFrameSource(BeginFrameSource* source) override;
   void SetExternalTilePriorityConstraints(
       const gfx::Rect& viewport_rect,
       const gfx::Transform& transform) override;
@@ skipping 462 matching lines @@
 
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_