Make IsSolidColor() a property on CC scrollbar layers.

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 cc14acf0e4883c6fb2a9c16b213c42de4b4a4719..85116d05216eb57b4df9c8e69f5784458a907059 100644
--- a/cc/layers/scrollbar_layer.h
+++ b/cc/layers/scrollbar_layer.h
@@ -23,7 +23,8 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
 
   static scoped_refptr<ScrollbarLayer> Create(
       scoped_ptr<Scrollbar> scrollbar,
-      int scroll_layer_id);
+      int scroll_layer_id,
+      bool is_solid_color);
 
   int scroll_layer_id() const { return scroll_layer_id_; }
   void SetScrollLayerId(int id);
@@ -31,6 +32,7 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
   virtual bool OpacityCanAnimateOnImplThread() const OVERRIDE;
 
   ScrollbarOrientation Orientation() const;
+  bool IsSolidColor() const;
 
   // Layer interface
   virtual void SetTexturePriorities(const PriorityCalculator& priority_calc)
@@ -52,7 +54,8 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
 
  protected:
   ScrollbarLayer(scoped_ptr<Scrollbar> scrollbar,
-                 int scroll_layer_id);
+                 int scroll_layer_id,
+                 bool is_solid_color);
   virtual ~ScrollbarLayer();
 
  private:
@@ -76,6 +79,7 @@ class CC_EXPORT ScrollbarLayer : public ContentsScalingLayer {
   int thumb_length_;
   gfx::Rect track_rect_;
   int scroll_layer_id_;
+  bool is_solid_color_;
 
   unsigned texture_format_;