Mac: Don't repaint scrollbars every frame

cc/trees/layer_tree_host.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_H_
 #define CC_TREES_LAYER_TREE_HOST_H_
 
 #include <limits>
 #include <set>
 #include <string>
@@ skipping 136 matching lines @@
   }
 
   void SetNeedsDisplayOnAllLayers();
 
   void CollectRenderingStats(RenderingStats* stats) const;
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation() const {
     return rendering_stats_instrumentation_.get();
   }
 
-  const RendererCapabilities& GetRendererCapabilities() const;
+  virtual const RendererCapabilities& GetRendererCapabilities() const;
 
   void SetNeedsAnimate();
   virtual void SetNeedsUpdateLayers();
   virtual void SetNeedsCommit();
   virtual void SetNeedsFullTreeSync();
   virtual void SetNeedsMetaInfoRecomputation(
       bool needs_meta_info_recomputation);
   void SetNeedsRedraw();
   void SetNeedsRedrawRect(const gfx::Rect& damage_rect);
   bool CommitRequested() const;
@@ skipping 332 matching lines @@
 
   uint32_t surface_id_namespace_;
   uint32_t next_surface_sequence_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_H_