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

Source/core/svg/SVGTitleElement.cpp

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 26 matching lines @@
 {
     return adoptRef(new SVGTitleElement(tagName, document));
 }
 
 Node::InsertionNotificationRequest SVGTitleElement::insertedInto(ContainerNode* rootParent)
 {
     SVGElement::insertedInto(rootParent);
     if (!rootParent->inDocument())
         return InsertionDone;
     if (firstChild())
-        document()->setTitleElement(textContent(), this);
+        document().setTitleElement(textContent(), this);
     return InsertionDone;
 }
 
 void SVGTitleElement::removedFrom(ContainerNode* rootParent)
 {
     SVGElement::removedFrom(rootParent);
     if (rootParent->inDocument())
-        document()->removeTitle(this);
+        document().removeTitle(this);
 }
 
 void SVGTitleElement::childrenChanged(bool changedByParser, Node* beforeChange, Node* afterChange, int childCountDelta)
 {
     SVGElement::childrenChanged(changedByParser, beforeChange, afterChange, childCountDelta);
     if (inDocument())
-        document()->setTitleElement(textContent(), this);
+        document().setTitleElement(textContent(), this);
 }
 
 }