Fix crash when scrolling in a remote process frame

third_party/WebKit/Source/core/page/scrolling/TopDocumentRootScrollerController.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 TopDocumentRootScrollerController_h
 #define TopDocumentRootScrollerController_h
 
 #include "core/CoreExport.h"
 #include "core/page/scrolling/RootScrollerController.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Element;
 class GraphicsLayer;
 class ScrollStateCallback;
 class ViewportScrollCallback;
 
 // The RootScrollerController used to manage the root scroller for the top
 // level Document on a page. In addition to the regular RootScroller duties,
 // such as keeping track of which Element is set as root scroller and which is
 // the effective root scroller, this class is also manages the "global" root
 // scroller. That is, given all the iframes on a page and their individual root
 // scrollers, this class will determine which ultimate Element should be used
 // as the root scroller and ensures that Element is used to scroll top controls
 // and provide overscroll effects.
 // TODO(bokan): This class is currently OOPIF unaware. It should be broken into
-// a standalone class and placed on a Page level object. crbug.com/505516
+// a standalone class and placed on a Page level object. crbug.com/642378.
 class CORE_EXPORT TopDocumentRootScrollerController
     : public RootScrollerController {
 public:
     static TopDocumentRootScrollerController* create(Document&);
 
     DECLARE_VIRTUAL_TRACE();
 
     // 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() override;
@@ skipping 36 matching lines @@
     Member<ViewportScrollCallback> m_viewportApplyScroll;
 
     // The page level root scroller. i.e. The actual element for which scrolling
     // should move top controls and produce overscroll glow.
     WeakMember<Element> m_globalRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h