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

Source/core/html/HTMLLinkElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google 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 88 matching lines @@
     };
 
     enum RemovePendingSheetNotificationType {
         RemovePendingSheetNotifyImmediately,
         RemovePendingSheetNotifyLater
     };
 
     void clearSheet();
     void addPendingSheet(PendingSheetType);
     void removePendingSheet(RemovePendingSheetNotificationType = RemovePendingSheetNotifyImmediately);
-    Document* document();
+    Document& document();
 
     ResourcePtr<CSSStyleSheetResource> m_resource;
     RefPtr<CSSStyleSheet> m_sheet;
     DisabledState m_disabledState;
     PendingSheetType m_pendingSheetType;
     bool m_loading;
     bool m_firedLoad;
     bool m_loadedSheet;
 };
 
@@ skipping 29 matching lines @@
     DOMSettableTokenList* sizes() const;
 
     void dispatchPendingEvent(LinkEventSender*);
     void scheduleEvent();
     static void dispatchPendingLoadEvents();
 
     // From LinkLoaderClient
     virtual bool shouldLoadLink() OVERRIDE;
 
     // For LinkStyle
-    bool loadLink(const String& type, const KURL& url) { return m_linkLoader.loadLink(m_relAttribute, type, url, document()); }
+    bool loadLink(const String& type, const KURL& url) { return m_linkLoader.loadLink(m_relAttribute, type, url, &document()); }
     bool isAlternate() const { return linkStyle()->isUnset() && m_relAttribute.isAlternate(); }
     bool shouldProcessStyle() { return linkResourceToProcess() && linkStyle(); }
 
 private:
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
 
     LinkStyle* linkStyle() const;
     LinkImport* linkImport() const;
     LinkResource* linkResourceToProcess();
 
@@ skipping 36 matching lines @@
 
 inline HTMLLinkElement* toHTMLLinkElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(HTMLNames::linkTag));
     return static_cast<HTMLLinkElement*>(node);
 }
 
 } //namespace
 
 #endif