Create abstract common base class for impl scrollbars.

cc/scrollbar_layer_impl.h

Index: cc/scrollbar_layer_impl.h
diff --git a/cc/scrollbar_layer_impl.h b/cc/scrollbar_layer_impl.h
index 57e07a748ec1ebaf5d77f9f2b85f32d8ba5922c4..e6c80db9583355290f91c16d8453c67da3cb7dee 100644
--- a/cc/scrollbar_layer_impl.h
+++ b/cc/scrollbar_layer_impl.h
@@ -6,17 +6,16 @@
 #define CC_SCROLLBAR_LAYER_IMPL_H_
 
 #include "cc/cc_export.h"
-#include "cc/layer_impl.h"
 #include "cc/scrollbar_geometry_fixed_thumb.h"
+#include "cc/scrollbar_layer_impl_base.h"
 #include <public/WebRect.h>
-#include <public/WebScrollbar.h>
 #include <public/WebVector.h>
 
 namespace cc {
 
 class ScrollView;
 
-class CC_EXPORT ScrollbarLayerImpl : public LayerImpl {
+class CC_EXPORT ScrollbarLayerImpl : public ScrollbarLayerImplBase {
 public:
     static scoped_ptr<ScrollbarLayerImpl> create(LayerTreeImpl* treeImpl, int id);
     virtual ~ScrollbarLayerImpl();
@@ -29,16 +28,16 @@ public:
     void setForeTrackResourceId(ResourceProvider::ResourceId id) { m_foreTrackResourceId = id; }
     void setThumbResourceId(ResourceProvider::ResourceId id) { m_thumbResourceId = id; }
 
-    float currentPos() const { return m_currentPos; }
+    virtual float currentPos() const OVERRIDE;
     void setCurrentPos(float currentPos) { m_currentPos = currentPos; }
 
-    int totalSize() const { return m_totalSize; }
+    virtual int totalSize() const OVERRIDE;
     void setTotalSize(int totalSize) { m_totalSize = totalSize; }
 
-    int maximum() const { return m_maximum; }
+    virtual int maximum() const OVERRIDE;
     void setMaximum(int maximum) { m_maximum = maximum; }
 
-    WebKit::WebScrollbar::Orientation orientation() const { return m_orientation; }
+    virtual WebKit::WebScrollbar::Orientation orientation() const OVERRIDE;
 
     virtual void appendQuads(QuadSink&, AppendQuadsData&) OVERRIDE;