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

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index b78cf1a45a80fb195489e303a64a0cea66d22a93..5b796663dc730016289a67056840442d3bdabe6a 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -622,7 +622,7 @@ scoped_ptr<LayerImpl> LayerImpl::TakeReplicaLayer() {
   return replica_layer_.Pass();
 }
 
-ScrollbarLayerImpl* LayerImpl::ToScrollbarLayer() {
+ScrollbarLayerImplBase* LayerImpl::ToScrollbarLayer() {
   return NULL;
 }
 
@@ -980,13 +980,14 @@ void LayerImpl::DidBecomeActive() {
   }
 }
 void LayerImpl::SetHorizontalScrollbarLayer(
-    ScrollbarLayerImpl* scrollbar_layer) {
+    ScrollbarLayerImplBase* scrollbar_layer) {
   horizontal_scrollbar_layer_ = scrollbar_layer;
   if (horizontal_scrollbar_layer_)
     horizontal_scrollbar_layer_->set_scroll_layer_id(id());
 }
 
-void LayerImpl::SetVerticalScrollbarLayer(ScrollbarLayerImpl* scrollbar_layer) {
+void LayerImpl::SetVerticalScrollbarLayer(
+    ScrollbarLayerImplBase* scrollbar_layer) {
   vertical_scrollbar_layer_ = scrollbar_layer;
   if (vertical_scrollbar_layer_)
     vertical_scrollbar_layer_->set_scroll_layer_id(id());