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

Source/core/html/FormAssociatedElement.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 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 145 matching lines @@
     m_form = 0;
     didChangeForm();
 }
 
 void FormAssociatedElement::resetFormOwner()
 {
     HTMLFormElement* originalForm = m_form;
     setForm(findAssociatedForm(toHTMLElement(this), m_form));
     HTMLElement* element = toHTMLElement(this);
     if (m_form && m_form != originalForm && m_form->inDocument())
-        element->document()->didAssociateFormControl(element);
+        element->document().didAssociateFormControl(element);
 }
 
 void FormAssociatedElement::formAttributeChanged()
 {
     HTMLElement* element = toHTMLElement(this);
     if (!element->fastHasAttribute(formAttr)) {
         // The form attribute removed. We need to reset form owner here.
         HTMLFormElement* originalForm = m_form;
         setForm(element->findFormAncestor());
         HTMLElement* element = toHTMLElement(this);
         if (m_form && m_form != originalForm && m_form->inDocument())
-            element->document()->didAssociateFormControl(element);
+            element->document().didAssociateFormControl(element);
         m_formAttributeTargetObserver = nullptr;
     } else {
         resetFormOwner();
         if (element->inDocument())
             resetFormAttributeTargetObserver();
     }
 }
 
 bool FormAssociatedElement::customError() const
 {
@@ skipping 110 matching lines @@
     , m_element(element)
 {
 }
 
 void FormAttributeTargetObserver::idTargetChanged()
 {
     m_element->formAttributeTargetChanged();
 }
 
 } // namespace Webcore