Make RootScroller set the outer viewport scroll layer in the compositor

content/renderer/gpu/render_widget_compositor.h

 // Copyright (c) 2013 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 CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 121 matching lines @@
       blink::WebLayoutAndPaintAsyncCallback* callback) override;
   void compositeAndReadbackAsync(
       blink::WebCompositeAndReadbackAsyncCallback* callback) override;
   void setDeferCommits(bool defer_commits) override;
   void registerViewportLayers(
       const blink::WebLayer* overscrollElasticityLayer,
       const blink::WebLayer* pageScaleLayer,
       const blink::WebLayer* innerViewportScrollLayer,
       const blink::WebLayer* outerViewportScrollLayer) override;
   void clearViewportLayers() override;
+  void setRootScrollerLayer(const blink::WebLayer* rootScrollerLayer) override;
   void registerSelection(const blink::WebSelection& selection) override;
   void clearSelection() override;
   void setMutatorClient(
       std::unique_ptr<blink::WebCompositorMutatorClient>) override;
   void setEventListenerProperties(
       blink::WebEventListenerClass eventClass,
       blink::WebEventListenerProperties properties) override;
   blink::WebEventListenerProperties eventListenerProperties(
       blink::WebEventListenerClass eventClass) const override;
   void setHaveScrollEventHandlers(bool) override;
@@ skipping 70 matching lines @@
   std::unique_ptr<cc::CopyOutputRequest> temporary_copy_output_request_;
 
   cc::RemoteProtoChannel::ProtoReceiver* remote_proto_channel_receiver_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_