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

cc/layers/scrollbar_layer.h

Index: cc/layers/scrollbar_layer.h
diff --git a/cc/layers/scrollbar_layer.h b/cc/layers/scrollbar_layer.h
index f500dcc66d277dd8d46e0e835239fb844e367a5f..8f27198fcb9dfbb2828a168c530f6986afe12642 100644
--- a/cc/layers/scrollbar_layer.h
+++ b/cc/layers/scrollbar_layer.h
@@ -8,6 +8,7 @@
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/contents_scaling_layer.h"
+#include "cc/layers/scrollbar_layer_base.h"
 #include "cc/layers/scrollbar_theme_painter.h"
 #include "cc/resources/layer_updater.h"
 
@@ -16,7 +17,8 @@ class CachingBitmapContentLayerUpdater;
 class ResourceUpdateQueue;
 class ScrollbarThemeComposite;
 
-class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
+class CC_EXPORT ScrollbarLayer : public ScrollbarLayerBase,
+                                 public ContentsScalingLayer {
  public:
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
@@ -25,12 +27,9 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
       scoped_ptr<Scrollbar> scrollbar,
       int scroll_layer_id);
 
-  int scroll_layer_id() const { return scroll_layer_id_; }
-  void SetScrollLayerId(int id);
-
   virtual bool OpacityCanAnimateOnImplThread() const OVERRIDE;
-
-  ScrollbarOrientation Orientation() const;
+  virtual ScrollbarLayerBase* ToScrollbarLayerBase() OVERRIDE;
+  virtual void SetScrollLayerId(int id) OVERRIDE;
 
   // Layer interface
   virtual void SetTexturePriorities(const PriorityCalculator& priority_calc)
@@ -47,8 +46,6 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
                                       float* contents_scale_y,
                                       gfx::Size* content_bounds) OVERRIDE;
 
-  virtual ScrollbarLayer* ToScrollbarLayer() OVERRIDE;
-
  protected:
   ScrollbarLayer(scoped_ptr<Scrollbar> scrollbar,
                  int scroll_layer_id);
@@ -73,7 +70,6 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
   int thumb_thickness_;
   int thumb_length_;
   gfx::Rect track_rect_;
-  int scroll_layer_id_;
 
   unsigned texture_format_;