Have LiveNodeListBase::ownerNode() return a reference

Source/core/dom/EmptyNodeList.h

 /*
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 22 matching lines @@
 #define EmptyNodeList_h
 
 #include "core/dom/NodeList.h"
 
 namespace WebCore {
 
 class EmptyNodeList FINAL : public NodeList {
 public:
     static PassRefPtr<EmptyNodeList> create(Node* rootNode)
     {
+        ASSERT(rootNode);
         return adoptRef(new EmptyNodeList(rootNode));
     }
     virtual ~EmptyNodeList();
 
-    Node* ownerNode() const { return m_owner.get(); }
+    Node& ownerNode() const { return *m_owner; }
 
 private:
     explicit EmptyNodeList(Node* rootNode) : m_owner(rootNode) { }
 
     virtual unsigned length() const OVERRIDE { return 0; }
     virtual Node* item(unsigned) const OVERRIDE { return 0; }
 
     virtual bool isEmptyNodeList() const OVERRIDE { return true; }
     virtual Node* virtualOwnerNode() const OVERRIDE;
 
     RefPtr<Node> m_owner;
 };
 
 DEFINE_TYPE_CASTS(EmptyNodeList, NodeList, nodeList, nodeList->isEmptyNodeList(), nodeList.isEmptyNodeList());
 
 } // namespace WebCore
 
 #endif // EmptyNodeList_h