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

Source/core/html/HTMLLabelElement.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) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 113 matching lines @@
     if (evt->type() == eventNames().clickEvent && !processingClick) {
         RefPtr<HTMLElement> element = control();
 
         // If we can't find a control or if the control received the click
         // event, then there's no need for us to do anything.
         if (!element || (evt->target() && element->containsIncludingShadowDOM(evt->target()->toNode())))
             return;
 
         processingClick = true;
 
-        document()->updateLayoutIgnorePendingStylesheets();
+        document().updateLayoutIgnorePendingStylesheets();
         if (element->isMouseFocusable())
             element->focus(true, FocusDirectionMouse);
 
         // Click the corresponding control.
         element->dispatchSimulatedClick(evt);
 
         processingClick = false;
 
         evt->setDefaultHandled();
     }
@@ skipping 20 matching lines @@
 
 void HTMLLabelElement::accessKeyAction(bool sendMouseEvents)
 {
     if (HTMLElement* element = control())
         element->accessKeyAction(sendMouseEvents);
     else
         HTMLElement::accessKeyAction(sendMouseEvents);
 }
 
 } // namespace