Make IsSolidColor() a property on CC scrollbar layers.

cc/test/fake_scrollbar_layer.h

 // Copyright 2012 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.
 
 #ifndef CC_TEST_FAKE_SCROLLBAR_LAYER_H_
 #define CC_TEST_FAKE_SCROLLBAR_LAYER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/layers/scrollbar_layer.h"
 
 namespace cc {
 
 class FakeScrollbarLayer : public ScrollbarLayer {
  public:
   static scoped_refptr<FakeScrollbarLayer> Create(bool paint_during_update,
                                                   bool has_thumb,
-                                                  int scrolling_layer_id) {
+                                                  int scrolling_layer_id,
+                                                  bool is_solid_color) {
     return make_scoped_refptr(new FakeScrollbarLayer(
-        paint_during_update, has_thumb, scrolling_layer_id));
+        paint_during_update, has_thumb, scrolling_layer_id, is_solid_color));
   }
 
   int update_count() const { return update_count_; }
   void reset_update_count() { update_count_ = 0; }
   size_t last_update_full_upload_size() const {
     return last_update_full_upload_size_;
   }
   size_t last_update_partial_upload_size() const {
     return last_update_partial_upload_size_;
   }
 
   virtual void Update(ResourceUpdateQueue* queue,
                       const OcclusionTracker* occlusion,
                       RenderingStats* stats) OVERRIDE;
 
  private:
   FakeScrollbarLayer(bool paint_during_update,
                      bool has_thumb,
-                     int scrolling_layer_id);
+                     int scrolling_layer_id,
+                     bool is_solid_color);
   virtual ~FakeScrollbarLayer();
 
   int update_count_;
   size_t last_update_full_upload_size_;
   size_t last_update_partial_upload_size_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_SCROLLBAR_LAYER_H_