Create abstract common base class for impl scrollbars.

cc/scrollbar_layer_impl_base.h

Index: cc/scrollbar_layer_impl_base.h
diff --git a/cc/scrollbar_layer_impl_base.h b/cc/scrollbar_layer_impl_base.h
new file mode 100644
index 0000000000000000000000000000000000000000..4a0f54ae77a8bed448eae03e6a21e712f4cb2eeb
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+++ b/cc/scrollbar_layer_impl_base.h
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+// 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_SCROLLBAR_LAYER_IMPL_BASE_H_
+#define CC_SCROLLBAR_LAYER_IMPL_BASE_H_
+
+#include "cc/cc_export.h"
+#include "cc/layer_impl.h"
+#include <public/WebScrollbar.h>
+
+namespace cc {
+
+class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
+public:
+    virtual ~ScrollbarLayerImplBase() { }
+
+    virtual float currentPos() const = 0;
+    virtual int totalSize() const = 0;
+    virtual int maximum() const = 0;
+    virtual WebKit::WebScrollbar::Orientation orientation() const = 0;
+
+protected:
+    ScrollbarLayerImplBase(LayerTreeImpl* treeImpl, int id)
+        : LayerImpl(treeImpl, id) { }
+
+};
+
+} // namespace cc
+#endif // CC_SCROLLBAR_LAYER_IMPL_BASE_H_