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

Source/core/accessibility/AccessibilityNodeObject.cpp

 /*
 * Copyright (C) 2012, Google 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
@@ skipping 1435 matching lines @@
             return toElement(node);
     }
 
     return 0;
 }
 
 Document* AccessibilityNodeObject::document() const
 {
     if (!node())
         return 0;
-    return node()->document();
+    return &node()->document();
 }
 
 void AccessibilityNodeObject::setNode(Node* node)
 {
     m_node = node;
 }
 
 AccessibilityObject* AccessibilityNodeObject::correspondingControlForLabelElement() const
 {
     HTMLLabelElement* labelElement = labelElementContainer();
@@ skipping 332 matching lines @@
         useTextUnderElement = true;
 
     if (useTextUnderElement) {
         String text = textUnderElement();
         if (!text.isEmpty())
             textOrder.append(AccessibilityText(text, ChildrenText));
     }
 }
 
 } // namespace WebCore