Disable overlay scrollbars in Blink when hidden by the compositor.

cc/layers/layer_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_LAYERS_LAYER_IMPL_H_
 #define CC_LAYERS_LAYER_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 561 matching lines @@
   std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
       owned_debug_info_;
   base::trace_event::ConvertableToTraceFormat* debug_info_;
   std::unique_ptr<RenderSurfaceImpl> render_surface_;
   gfx::Size preferred_raster_bounds_;
 
   bool has_preferred_raster_bounds_ : 1;
   bool scrolls_drawn_descendant_ : 1;
   bool has_will_change_transform_hint_ : 1;
   bool needs_push_properties_ : 1;
+  bool scrollbars_hidden_ : 1;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_