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

Source/core/accessibility/AccessibilityListBox.cpp

 /*
  * Copyright (C) 2008 Apple 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
@@ skipping 111 matching lines @@
             result.append(m_children[i]);
     }
 }
 
 AccessibilityObject* AccessibilityListBox::listBoxOptionAccessibilityObject(HTMLElement* element) const
 {
     // skip hr elements
     if (!element || element->hasTagName(hrTag))
         return 0;
 
-    AccessibilityObject* listBoxObject = m_renderer->document()->axObjectCache()->getOrCreate(ListBoxOptionRole);
+    AccessibilityObject* listBoxObject = m_renderer->document().axObjectCache()->getOrCreate(ListBoxOptionRole);
     static_cast<AccessibilityListBoxOption*>(listBoxObject)->setHTMLElement(element);
 
     return listBoxObject;
 }
 
 AccessibilityObject* AccessibilityListBox::elementAccessibilityHitTest(const IntPoint& point) const
 {
     // the internal HTMLSelectElement methods for returning a listbox option at a point
     // ignore optgroup elements.
     if (!m_renderer)
@@ skipping 17 matching lines @@
         }
     }
 
     if (listBoxOption && !listBoxOption->accessibilityIsIgnored())
         return listBoxOption;
 
     return axObjectCache()->getOrCreate(m_renderer);
 }
 
 } // namespace WebCore