Have Node::document() return a reference instead of a pointer

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 8157bfcb4e9e51ab97112a31545eaff3fd13c9a1..5aadeae401b461b158d7aacd1f310c7bdfa7db53 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -484,14 +484,12 @@ public:
     // of a Document node.
     Document* ownerDocument() const;
 
-    // FIXME: This should return a reference.
-    // Returns the document associated with this node. This method never returns 0.
-    // A Document node returns itself.
-    Document* document() const
+    // Returns the document associated with this node. A Document node returns itself.
+    Document& document() const
     {
         ASSERT(this);
         ASSERT(documentInternal());
-        return documentInternal();
+        return *documentInternal();
     }
 
     TreeScope* treeScope() const { return m_treeScope; }