Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

webkit/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 WebScrollbarLayerImpl_h
 #define WebScrollbarLayerImpl_h
 
 #include "base/memory/scoped_ptr.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebScrollbarLayer.h"
 #include "webkit/compositor_bindings/webkit_compositor_bindings_export.h"
 
 namespace WebKit {
 class WebLayerImpl;
 
 class WebScrollbarLayerImpl : public WebScrollbarLayer {
 public:
     WEBKIT_COMPOSITOR_BINDINGS_EXPORT WebScrollbarLayerImpl(
         WebScrollbar*, WebScrollbarThemePainter, WebScrollbarThemeGeometry*);
     virtual ~WebScrollbarLayerImpl();
 
     // WebScrollbarLayer implementation.
     virtual WebLayer* layer() OVERRIDE;
     virtual void setScrollLayer(WebLayer*) OVERRIDE;
 
+    WEBKIT_COMPOSITOR_BINDINGS_EXPORT static void setDefaultGeometry(WebScrollbarThemeGeometry*);
+    WEBKIT_COMPOSITOR_BINDINGS_EXPORT static void setDefaultUsesOverlayScrollbars(bool);
+
 private:
     scoped_ptr<WebLayerImpl> m_layer;
 };
 
 }
 
 #endif // WebScrollbarLayerImpl_h