Add viewport scrollbar class to support overlay scrollbars for pinch zoom virtual viewport.

webkit/renderer/compositor_bindings/web_scrollbar_layer_impl.h

 // 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 WEBKIT_RENDERER_COMPOSITOR_BINDINGS_WEB_SCROLLBAR_LAYER_IMPL_H_
 #define WEBKIT_RENDERER_COMPOSITOR_BINDINGS_WEB_SCROLLBAR_LAYER_IMPL_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "third_party/WebKit/public/platform/WebScrollbar.h"
 #include "third_party/WebKit/public/platform/WebScrollbarLayer.h"
+#include "webkit/renderer/compositor_bindings/web_layer_impl.h"
 #include "webkit/renderer/compositor_bindings/webkit_compositor_bindings_export.h"
 
 namespace WebKit {
-class WebScrollbar;
 class WebScrollbarThemeGeometry;
 class WebScrollbarThemePainter;
 }
 
 namespace webkit {
 
 class WebLayerImpl;
 
 class WebScrollbarLayerImpl : public WebKit::WebScrollbarLayer {
  public:
   WEBKIT_COMPOSITOR_BINDINGS_EXPORT WebScrollbarLayerImpl(
       WebKit::WebScrollbar* scrollbar,
       WebKit::WebScrollbarThemePainter painter,
       WebKit::WebScrollbarThemeGeometry* geometry);
+  WEBKIT_COMPOSITOR_BINDINGS_EXPORT WebScrollbarLayerImpl(
+      WebKit::WebLayer* scroll_layer,
+      WebKit::WebScrollbar::Orientation orientation,
+      size_t thickness);
   virtual ~WebScrollbarLayerImpl();
 
   // WebKit::WebScrollbarLayer implementation.
   virtual WebKit::WebLayer* layer();
   virtual void setScrollLayer(WebKit::WebLayer* layer);
 
  private:
   scoped_ptr<WebLayerImpl> layer_;
 
   DISALLOW_COPY_AND_ASSIGN(WebScrollbarLayerImpl);
 };
 
 }  // namespace webkit
 
 #endif  // WEBKIT_RENDERER_COMPOSITOR_BINDINGS_WEB_SCROLLBAR_LAYER_IMPL_H_