cc : Initialize solid color scrollbar layer on main thread to 0.

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 110 matching lines @@
   void SetMasksToBounds(bool masks_to_bounds);
   bool masks_to_bounds() const { return masks_to_bounds_; }
 
   void SetMaskLayer(Layer* mask_layer);
   Layer* mask_layer() { return mask_layer_.get(); }
   const Layer* mask_layer() const { return mask_layer_.get(); }
 
   virtual void SetNeedsDisplayRect(const gfx::Rect& dirty_rect);
   void SetNeedsDisplay() { SetNeedsDisplayRect(gfx::Rect(bounds())); }
 
-  void SetOpacity(float opacity);
+  virtual void SetOpacity(float opacity);
   float opacity() const { return opacity_; }
   float EffectiveOpacity() const;
   bool OpacityIsAnimating() const;
   bool HasPotentiallyRunningOpacityAnimation() const;
   virtual bool OpacityCanAnimateOnImplThread() const;
 
   virtual bool AlwaysUseActiveTreeOpacity() const;
 
   void SetBlendMode(SkXfermode::Mode blend_mode);
   SkXfermode::Mode blend_mode() const { return blend_mode_; }
@@ skipping 538 matching lines @@
   // 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_