Make RootScroller set the outer viewport scroll layer in the compositor

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h

 // Copyright 2016 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 RootScrollerController_h
 #define RootScrollerController_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Element;
+class GraphicsLayer;
 class ViewportScrollCallback;
 
 // Manages the root scroller associated with a given document. The root scroller
 // causes top controls movement, overscroll effects and prevents chaining
 // scrolls up further in the DOM. It can be set from script using
 // document.setRootScroller.
 //
 // There are two notions of a root scroller in this class: m_rootScroller and
 // m_effectiveRootScroller. The former is the Element that was set as the root
 // scroller using document.setRootScroller. If the page didn't set a root
@@ skipping 38 matching lines @@
     // This returns the Element that's actually being used to control viewport
     // actions right now. This is different from get() if a root scroller hasn't
     // been set, or if the set root scroller isn't currently a valid scroller.
     Element* effectiveRootScroller() const;
 
     // This class needs to be informed of changes in layout so that it can
     // determine if the current root scroller is still valid or if it must be
     // replaced by the defualt root scroller.
     void didUpdateLayout();
 
+    // This class needs to be informed of changes to compositing so that it can
+    // update the compositor when the effective root scroller changes.
+    void didUpdateCompositing();
+
+    GraphicsLayer* rootScrollerLayer();
+
     // TODO(bokan): Temporarily exposed to allow ScrollCustomization to
     // differentiate between real custom callback and the built-in viewport
     // apply scroll.
     const ViewportScrollCallback* viewportScrollCallback()
     {
         return m_viewportApplyScroll;
     }
 
     void setViewportScrollCallback(ViewportScrollCallback*);
 
@@ skipping 18 matching lines @@
     // m_viewportApplyScroll has been set, this element is guaranteed to have it
     // set as its applyScroll callback. This can be nullptr during
     // initialization and will not be set until m_viewportApplyScroll is
     // provided.
     WeakMember<Element> m_effectiveRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h