Make RootScroller set the outer viewport scroll layer in the compositor

content/renderer/gpu/render_widget_compositor.cc

 // 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.
 
 #include "content/renderer/gpu/render_widget_compositor.h"
 
 #include <stddef.h>
 #include <limits>
 #include <string>
 #include <utility>
@@ skipping 764 matching lines @@
 
 void RenderWidgetCompositor::registerViewportLayers(
     const blink::WebLayer* overscrollElasticityLayer,
     const blink::WebLayer* pageScaleLayer,
     const blink::WebLayer* innerViewportScrollLayer,
     const blink::WebLayer* outerViewportScrollLayer) {
   layer_tree_host_->RegisterViewportLayers(
       // TODO(bokan): This check can probably be removed now, but it looks
       // like overscroll elasticity may still be NULL until VisualViewport
       // registers its layers.
-      // The scroll elasticity layer will only exist when using pinch virtual
-      // viewports.
       overscrollElasticityLayer
           ? static_cast<const cc_blink::WebLayerImpl*>(
                 overscrollElasticityLayer)->layer()
           : NULL,
       static_cast<const cc_blink::WebLayerImpl*>(pageScaleLayer)->layer(),
       static_cast<const cc_blink::WebLayerImpl*>(innerViewportScrollLayer)
           ->layer(),
       // TODO(bokan): This check can probably be removed now, but it looks
-      // like overscroll elasticity may still be NULL until VisualViewport
+      // like outer viewport may still be NULL until VisualViewport
       // registers its layers.
-      // The outer viewport layer will only exist when using pinch virtual
-      // viewports.
       outerViewportScrollLayer
           ? static_cast<const cc_blink::WebLayerImpl*>(outerViewportScrollLayer)
                 ->layer()
           : NULL);
 }
 
 void RenderWidgetCompositor::clearViewportLayers() {
   layer_tree_host_->RegisterViewportLayers(
       scoped_refptr<cc::Layer>(), scoped_refptr<cc::Layer>(),
       scoped_refptr<cc::Layer>(), scoped_refptr<cc::Layer>());
 }
 
+void RenderWidgetCompositor::setRootScrollerLayer(
+    const blink::WebLayer* rootScrollerLayer) {
+  layer_tree_host_->SetRootScrollerLayer(rootScrollerLayer
+      ? static_cast<const cc_blink::WebLayerImpl*>(rootScrollerLayer)->layer()
+      : NULL);
+}
+
 void RenderWidgetCompositor::registerSelection(
     const blink::WebSelection& selection) {
   layer_tree_host_->RegisterSelection(ConvertWebSelection(selection));
 }
 
 void RenderWidgetCompositor::clearSelection() {
   cc::LayerSelection empty_selection;
   layer_tree_host_->RegisterSelection(empty_selection);
 }
 
@@ skipping 323 matching lines @@
 
   remote_proto_channel_receiver_->OnProtoReceived(std::move(deserialized));
 }
 
 void RenderWidgetCompositor::SetPaintedDeviceScaleFactor(
     float device_scale) {
   layer_tree_host_->SetPaintedDeviceScaleFactor(device_scale);
 }
 
 }  // namespace content