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

Source/core/html/ClassList.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 45 matching lines @@
 }
 
 bool ClassList::containsInternal(const AtomicString& token) const
 {
     return m_element->hasClass() && classNames().contains(token);
 }
 
 const SpaceSplitString& ClassList::classNames() const
 {
     ASSERT(m_element->hasClass());
-    if (m_element->document()->inQuirksMode()) {
+    if (m_element->document().inQuirksMode()) {
         if (!m_classNamesForQuirksMode)
             m_classNamesForQuirksMode = adoptPtr(new SpaceSplitString(value(), false));
         return *m_classNamesForQuirksMode.get();
     }
     return m_element->elementData()->classNames();
 }
 
 } // namespace WebCore