Make IsSolidColor() a property on CC scrollbar layers.

cc/test/fake_scrollbar_layer.h

Index: cc/test/fake_scrollbar_layer.h
diff --git a/cc/test/fake_scrollbar_layer.h b/cc/test/fake_scrollbar_layer.h
index f06f752bc8a426944da0d54b2659bc4d3ff6c219..72ea3680126da64ba24e027d62f6bfa2fa5068dd 100644
--- a/cc/test/fake_scrollbar_layer.h
+++ b/cc/test/fake_scrollbar_layer.h
@@ -14,9 +14,10 @@ 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_; }
@@ -35,7 +36,8 @@ class FakeScrollbarLayer : public ScrollbarLayer {
  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_;