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

webkit/renderer/compositor_bindings/web_compositor_support_impl.h

 // Copyright (c) 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_COMPOSITOR_SUPPORT_IMPL_H_
 #define WEBKIT_RENDERER_COMPOSITOR_BINDINGS_WEB_COMPOSITOR_SUPPORT_IMPL_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "third_party/WebKit/public/platform/WebCompositorSupport.h"
 #include "third_party/WebKit/public/platform/WebLayer.h"
+#include "third_party/WebKit/public/platform/WebScrollbar.h"
 #include "third_party/WebKit/public/platform/WebTransformOperations.h"
 
 namespace WebKit {
 class WebGraphicsContext3D;
 }
 
 namespace webkit {
 
 class WebCompositorSupportImpl : public WebKit::WebCompositorSupport {
  public:
   WebCompositorSupportImpl();
   virtual ~WebCompositorSupportImpl();
 
   virtual WebKit::WebLayer* createLayer();
   virtual WebKit::WebContentLayer* createContentLayer(
       WebKit::WebContentLayerClient* client);
   virtual WebKit::WebExternalTextureLayer* createExternalTextureLayer(
       WebKit::WebExternalTextureLayerClient* client);
   virtual WebKit::WebExternalTextureLayer*
       createExternalTextureLayerForMailbox(
           WebKit::WebExternalTextureLayerClient* client);
   virtual WebKit::WebImageLayer* createImageLayer();
   virtual WebKit::WebSolidColorLayer* createSolidColorLayer();
   virtual WebKit::WebScrollbarLayer* createScrollbarLayer(
       WebKit::WebScrollbar* scrollbar,
       WebKit::WebScrollbarThemePainter painter,
       WebKit::WebScrollbarThemeGeometry*);
+  virtual WebKit::WebScrollbarLayer* createScrollbarLayer(

[enne (OOO), 2013/06/14 20:56:59]

I had a conversation with jamesr who suggested that cc create these scrollbar
layers itself based on layer ids passed into LayerTreeHost.  That way we don't
have to plumb these special scrollbar types all the way through compositor
bindings.  That seems like a better approach to me too.

[wjmaclean, 2013/06/17 13:44:28]

Yes, I will remove the compositor bindings parts, and put up a new CL.

+      WebKit::WebLayer* scroll_layer,
+      WebKit::WebScrollbar::Orientation orientation,
+      size_t thickness);
   virtual WebKit::WebAnimation* createAnimation(
       const WebKit::WebAnimationCurve& curve,
       WebKit::WebAnimation::TargetProperty target,
       int animation_id);
   virtual WebKit::WebFloatAnimationCurve* createFloatAnimationCurve();
   virtual WebKit::WebTransformAnimationCurve* createTransformAnimationCurve();
   virtual WebKit::WebTransformOperations* createTransformOperations();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(WebCompositorSupportImpl);
 };
 
 }  // namespace webkit
 
 #endif  // WEBKIT_RENDERER_COMPOSITOR_BINDINGS_WEB_COMPOSITOR_SUPPORT_IMPL_H_