Make RootScroller set the outer viewport scroll layer in the compositor

third_party/WebKit/public/platform/WebLayerTreeView.h

Index: third_party/WebKit/public/platform/WebLayerTreeView.h
diff --git a/third_party/WebKit/public/platform/WebLayerTreeView.h b/third_party/WebKit/public/platform/WebLayerTreeView.h
index 6c8770c4bbaa31af09eaa95e04da0a3c680538c3..19f3a68b5b73a63d1827eac79516fa789fbb0ea3 100644
--- a/third_party/WebKit/public/platform/WebLayerTreeView.h
+++ b/third_party/WebKit/public/platform/WebLayerTreeView.h
@@ -134,7 +134,7 @@ public:
     // Prevents updates to layer tree from becoming visible.
     virtual void setDeferCommits(bool deferCommits) { }
 
-    // Identify key layers to the compositor when using the pinch virtual viewport.
+    // Identify key layers to the compositor.
     virtual void registerViewportLayers(
         const WebLayer* overscrollElasticityLayer,
         const WebLayer* pageScaleLayer,
@@ -142,6 +142,11 @@ public:
         const WebLayer* outerViewportScrollLayer) { }
     virtual void clearViewportLayers() { }
 
+    // Identify the "root scroller" layer. This is the layer whose scrolling
+    // causes actions like overscroll glow and top controls movement and can be
+    // author defined using the rootScroller API.
+    virtual void setRootScrollerLayer(const WebLayer* rootScrollerLayer) { }
+
     // Used to update the active selection bounds.
     virtual void registerSelection(const WebSelection&) { }
     virtual void clearSelection() { }