Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

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 421 matching lines @@
 
   void SetHasWillChangeTransformHint(bool has_will_change);
   bool has_will_change_transform_hint() const {
     return has_will_change_transform_hint_;
   }
 
   MutatorHost* GetMutatorHost() const;
 
   ElementListType GetElementTypeForAnimation() const;
 
+  void set_needs_show_scrollbars(bool yes) { needs_show_scrollbars_ = yes; }
+  bool needs_show_scrollbars() { return needs_show_scrollbars_; }
+
  protected:
   LayerImpl(LayerTreeImpl* layer_impl,
             int id,
             scoped_refptr<SyncedScrollOffset> scroll_offset);
   LayerImpl(LayerTreeImpl* layer_impl, int id);
 
   // Get the color and size of the layer's debug border.
   virtual void GetDebugBorderProperties(SkColor* color, float* width) const;
 
   void AppendDebugBorderQuad(RenderPass* render_pass,
@@ skipping 97 matching lines @@
   PerformanceProperties<LayerImpl> performance_properties_;
 
   std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
       owned_debug_info_;
   base::trace_event::ConvertableToTraceFormat* debug_info_;
 
   bool has_will_change_transform_hint_ : 1;
   bool needs_push_properties_ : 1;
   bool scrollbars_hidden_ : 1;
 
+  // The needs_show_scrollbars_ bit tracks a pending request from Blink to show
+  // the overlay scrollbars. It's set on the scroll layer (not the scrollbar
+  // layers) and consumed by LayerTreeImpl::PushPropertiesTo during activation.
+  bool needs_show_scrollbars_ : 1;
+
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_