Create abstract common base class for impl scrollbars.

cc/scrollbar_layer_impl.cc

Index: cc/scrollbar_layer_impl.cc
diff --git a/cc/scrollbar_layer_impl.cc b/cc/scrollbar_layer_impl.cc
index 2f49176334470b6c7c8f49c3f0add2f997129259..f2996310d95eefb44b98d1fa8f890f52b746a522 100644
--- a/cc/scrollbar_layer_impl.cc
+++ b/cc/scrollbar_layer_impl.cc
@@ -20,7 +20,7 @@ scoped_ptr<ScrollbarLayerImpl> ScrollbarLayerImpl::create(LayerTreeImpl* treeImp
 }
 
 ScrollbarLayerImpl::ScrollbarLayerImpl(LayerTreeImpl* treeImpl, int id)
-    : LayerImpl(treeImpl, id)
+    : ScrollbarLayerImplBase(treeImpl, id)
     , m_scrollbar(this)
     , m_backTrackResourceId(0)
     , m_foreTrackResourceId(0)
@@ -65,6 +65,26 @@ void ScrollbarLayerImpl::setScrollbarData(WebScrollbar* scrollbar)
     m_geometry->update(scrollbar);
 }
 
+float ScrollbarLayerImpl::currentPos() const
+{
+    return m_currentPos;
+}
+
+int ScrollbarLayerImpl::totalSize() const
+{
+    return m_totalSize;
+}
+
+int ScrollbarLayerImpl::maximum() const
+{
+    return m_maximum;
+}
+
+WebKit::WebScrollbar::Orientation ScrollbarLayerImpl::orientation() const
+{
+    return m_orientation;
+}
+
 static gfx::RectF toUVRect(const gfx::Rect& r, const gfx::Rect& bounds)
 {
     return gfx::ScaleRect(r, 1.0 / bounds.width(), 1.0 / bounds.height());