Have Node::highestAncestor() return a reference

Source/core/dom/Node.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 265 matching lines @@
     ShadowRoot* containingShadowRoot() const;
     ShadowRoot* youngestShadowRoot() const;
 
     // Returns 0, a child of ShadowRoot, or a legacy shadow root.
     Node* nonBoundaryShadowTreeRootNode();
 
     // Node's parent, shadow tree host.
     ContainerNode* parentOrShadowHostNode() const;
     Element* parentOrShadowHostElement() const;
     void setParentOrShadowHostNode(ContainerNode*);
-    Node* highestAncestor() const;
+    Node& highestAncestor() const;
 
     // Knows about all kinds of hosts.
     ContainerNode* parentOrShadowHostOrTemplateHostNode() const;
 
     // Returns the parent node, but 0 if the parent node is a ShadowRoot.
     ContainerNode* nonShadowBoundaryParentNode() const;
 
     bool selfOrAncestorHasDirAutoAttribute() const { return getFlag(SelfOrAncestorHasDirAutoFlag); }
     void setSelfOrAncestorHasDirAutoAttribute(bool flag) { setFlag(flag, SelfOrAncestorHasDirAutoFlag); }
 
@@ skipping 610 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const WebCore::Node*);
 void showNodePath(const WebCore::Node*);
 #endif
 
 #endif