Have NodeWithIndex deal with references instead of pointers

Source/core/dom/NodeWithIndex.h

Index: Source/core/dom/NodeWithIndex.h
diff --git a/Source/core/dom/NodeWithIndex.h b/Source/core/dom/NodeWithIndex.h
index 8c75ccc86822b00b93cbf5030da24cabea7d82a3..02b6d33c15acdadcd3abdffe27003c6f37e2500e 100644
--- a/Source/core/dom/NodeWithIndex.h
+++ b/Source/core/dom/NodeWithIndex.h
@@ -34,27 +34,26 @@ namespace WebCore {
 // 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;
 };