Have NodeWithIndex deal with references instead of pointers

Source/core/dom/NodeWithIndex.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 16 matching lines @@
 #define NodeWithIndex_h
 
 #include "core/dom/Node.h"
 
 namespace WebCore {
 
 // For use when you want to get the index for a node repeatedly and
 // only want to walk the child list to figure out the index once.
 class NodeWithIndex {
 public:
-    explicit NodeWithIndex(Node* node)
+    explicit NodeWithIndex(Node& node)
         : m_node(node)
         , m_haveIndex(false)
     {
-        ASSERT(node);
     }
 
-    Node* node() const { return m_node; }
+    Node& node() const { return m_node; }
 
     int index() const
     {
         if (!m_haveIndex) {
-            m_index = m_node->nodeIndex();
+            m_index = m_node.nodeIndex();
             m_haveIndex = true;
         }
-        ASSERT(m_index == static_cast<int>(m_node->nodeIndex()));
+        ASSERT(m_index == static_cast<int>(m_node.nodeIndex()));
         return m_index;
     }
 
 private:
-    Node* m_node;
+    Node& m_node;
     mutable bool m_haveIndex;
     mutable int m_index;
 };
 
 }
 
 #endif