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 480cee0db3683360c8419e65cc2c564d09ca2c90..6a2747dee5801f68f3a020f71fb646b9d70bdb26 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;
 }
 
@@ -831,14 +831,14 @@ void LayerImpl::UpdateScrollbarPositions() {
   gfx::SizeF scrollable_size(max_scroll_offset_.x() + bounds_.width(),
                              max_scroll_offset_.y() + bounds_.height());
   if (horizontal_scrollbar_layer_) {
-    horizontal_scrollbar_layer_->SetCurrentPos(current_offset.x());
-    horizontal_scrollbar_layer_->SetMaximum(max_scroll_offset_.x());
+    horizontal_scrollbar_layer_->set_current_pos(current_offset.x());
+    horizontal_scrollbar_layer_->set_maximum(max_scroll_offset_.x());
     horizontal_scrollbar_layer_->set_visible_to_total_length_ratio(
         viewport.width() / scrollable_size.width());
   }
   if (vertical_scrollbar_layer_) {
-    vertical_scrollbar_layer_->SetCurrentPos(current_offset.y());
-    vertical_scrollbar_layer_->SetMaximum(max_scroll_offset_.y());
+    vertical_scrollbar_layer_->set_current_pos(current_offset.y());
+    vertical_scrollbar_layer_->set_maximum(max_scroll_offset_.y());
     vertical_scrollbar_layer_->set_visible_to_total_length_ratio(
         viewport.height() / scrollable_size.height());
   }
@@ -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());