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

Source/core/html/HTMLTitleElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2010 Apple Inc. All rights reserved.
  *
  * 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.
@@ skipping 34 matching lines @@
 
 PassRefPtr<HTMLTitleElement> HTMLTitleElement::create(const QualifiedName& tagName, Document* document)
 {
     return adoptRef(new HTMLTitleElement(tagName, document));
 }
 
 Node::InsertionNotificationRequest HTMLTitleElement::insertedInto(ContainerNode* insertionPoint)
 {
     HTMLElement::insertedInto(insertionPoint);
     if (inDocument() && !isInShadowTree())
-        document()->setTitleElement(text(), this);
+        document().setTitleElement(text(), this);
     return InsertionDone;
 }
 
 void HTMLTitleElement::removedFrom(ContainerNode* insertionPoint)
 {
     HTMLElement::removedFrom(insertionPoint);
     if (insertionPoint->inDocument() && !insertionPoint->isInShadowTree())
-        document()->removeTitle(this);
+        document().removeTitle(this);
 }
 
 void HTMLTitleElement::childrenChanged(bool changedByParser, Node* beforeChange, Node* afterChange, int childCountDelta)
 {
     HTMLElement::childrenChanged(changedByParser, beforeChange, afterChange, childCountDelta);
     if (inDocument() && !isInShadowTree())
-        document()->setTitleElement(text(), this);
+        document().setTitleElement(text(), this);
 }
 
 String HTMLTitleElement::text() const
 {
     StringBuilder result;
 
     for (Node *n = firstChild(); n; n = n->nextSibling()) {
         if (n->isTextNode())
             result.append(toText(n)->data());
     }
@@ skipping 11 matching lines @@
         toText(firstChild())->setData(value);
     else {
         // We make a copy here because entity of "value" argument can be Document::m_title,
         // which goes empty during removeChildren() invocation below,
         // which causes HTMLTitleElement::childrenChanged(), which ends up Document::setTitle().
         String valueCopy(value);
 
         if (numChildren > 0)
             removeChildren();
 
-        appendChild(document()->createTextNode(valueCopy.impl()), IGNORE_EXCEPTION);
+        appendChild(document().createTextNode(valueCopy.impl()), IGNORE_EXCEPTION);
     }
 }
 
 }