Make RootScroller set the outer viewport scroll layer in the compositor

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index 68349ec2b9a32e57b40da8c439d932b2b618474a..811e128a799f60c98daecf3d264c1bc37e733696 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -139,6 +139,7 @@ class CONTENT_EXPORT RenderWidgetCompositor
       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(