Disable overlay scrollbars in Blink when hidden by the compositor.

cc/layers/layer.h

 // 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.
 
 #ifndef CC_LAYERS_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 482 matching lines @@
   void ClearPreferredRasterBounds();
 
   AnimationHost* GetAnimationHost() const;
 
   ElementListType GetElementTypeForAnimation() const;
 
   // Tests in remote mode need to explicitly set the layer id so it matches the
   // layer id for the corresponding Layer on the engine.
   void SetLayerIdForTesting(int id);
 
+  void SetScrollbarsHiddenFromImplSide(bool hidden);
+
  protected:
   friend class LayerImpl;
   friend class TreeSynchronizer;
   virtual ~Layer();
   Layer();
 
   LayerTreeHost* layer_tree_host() { return layer_tree_host_; }
 
   // These SetNeeds functions are in order of severity of update:
   //
@@ skipping 201 matching lines @@
   int scroll_tree_index_;
   int property_tree_sequence_number_;
   gfx::Vector2dF offset_to_transform_parent_;
   bool should_flatten_transform_from_property_tree_ : 1;
   bool draws_content_ : 1;
   bool use_local_transform_for_backface_visibility_ : 1;
   bool should_check_backface_visibility_ : 1;
   bool force_render_surface_for_testing_ : 1;
   bool subtree_property_changed_ : 1;
   bool may_contain_video_ : 1;
+  bool scrollbars_hidden_ : 1;
   SkColor safe_opaque_background_color_;
   // draw_blend_mode may be different than blend_mode_,
   // when a RenderSurface re-parents the layer's blend_mode.
   SkXfermode::Mode draw_blend_mode_;
   std::unique_ptr<std::set<Layer*>> scroll_children_;
 
   std::unique_ptr<std::set<Layer*>> clip_children_;
 
   PaintProperties paint_properties_;
 
   // These all act like draw properties, so don't need push properties.
   gfx::Rect visible_layer_rect_;
   size_t num_unclipped_descendants_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_