Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/dom/ChildNodeList.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, 2007 Apple Inc. All rights reserved.
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 13 matching lines @@
 #ifndef ChildNodeList_h
 #define ChildNodeList_h
 
 #include "core/dom/LiveNodeList.h"
 #include "wtf/PassRefPtr.h"
 
 namespace WebCore {
 
 class ChildNodeList FINAL : public LiveNodeList {
 public:
-    static PassRefPtr<ChildNodeList> create(PassRefPtr<Node> rootNode)
+    static PassRefPtr<ChildNodeList> create(PassRefPtr<ContainerNode> rootNode)
     {
         return adoptRef(new ChildNodeList(rootNode));
     }
 
     virtual ~ChildNodeList();
 
 protected:
-    explicit ChildNodeList(PassRefPtr<Node> rootNode);
+    explicit ChildNodeList(PassRefPtr<ContainerNode> rootNode);
 
+    virtual bool isChildNodeList() const OVERRIDE { return true; }
     virtual bool nodeMatches(const Element&) const OVERRIDE;
 };
 
+DEFINE_TYPE_CASTS(ChildNodeList, NodeList, nodeList, nodeList->isChildNodeList(), nodeList.isChildNodeList());
+
 } // namespace WebCore
 
 #endif // ChildNodeList_h