Refactor cc scrollbar layers to separate solid-color vs desktop.

cc/layers/layer.cc

 // 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.
 
 #include "cc/layers/layer.h"
 
 #include <algorithm>
 
 #include "base/location.h"
 #include "base/metrics/histogram.h"
@@ skipping 949 matching lines @@
     LayerAnimationEventObserver* animation_observer) {
   layer_animation_controller_->RemoveEventObserver(animation_observer);
 }
 
 Region Layer::VisibleContentOpaqueRegion() const {
   if (contents_opaque())
     return visible_content_rect();
   return Region();
 }
 
-ScrollbarLayer* Layer::ToScrollbarLayer() {
+ScrollbarLayerInterface* Layer::ToScrollbarLayer() {
   return NULL;
 }
 
 RenderingStatsInstrumentation* Layer::rendering_stats_instrumentation() const {
   return layer_tree_host_->rendering_stats_instrumentation();
 }
 
 bool Layer::SupportsLCDText() const {
   return false;
 }
 
 }  // namespace cc