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

cc/layers/scrollbar_layer_base.h

+// Copyright 2013 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_LAYERS_SCROLLBAR_LAYER_BASE_H_
+#define CC_LAYERS_SCROLLBAR_LAYER_BASE_H_
+
+#include "cc/input/scrollbar.h"
+
+namespace cc {
+
+class Layer;
+
+class ScrollbarLayerBase {
+ public:
+  int scroll_layer_id() const { return scroll_layer_id_; }
+  virtual void SetScrollLayerId(int id) = 0;
+
+  ScrollbarOrientation orientation() const { return orientation_; }
+
+ protected:
+  ScrollbarLayerBase(int scroll_layer_id,
+                     ScrollbarOrientation orientation)
+      : scroll_layer_id_(scroll_layer_id),
+        orientation_(orientation) {}
+  virtual ~ScrollbarLayerBase() {}
+
+  // This member is set through the derived classes.
+  int scroll_layer_id_;
+
+ private:
+  ScrollbarOrientation orientation_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerBase);
+};
+
+}  // namespace cc
+
+#endif  // CC_LAYERS_SCROLLBAR_LAYER_BASE_H_