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

Source/core/svg/SVGElementInstance.cpp

 /*
  * Copyright (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2011 Torch Mobile (Beijing) Co. Ltd. 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 177 matching lines @@
         ASSERT((*it)->shadowTreeElement()->correspondingElement() == (*it)->correspondingElement());
         ASSERT((*it)->correspondingElement() == element);
         (*it)->shadowTreeElement()->setCorrespondingElement(0);
 
         if (SVGUseElement* element = (*it)->correspondingUseElement()) {
             ASSERT(element->inDocument());
             element->invalidateShadowTree();
         }
     }
 
-    element->document()->updateStyleIfNeeded();
+    element->document().updateStyleIfNeeded();
 }
 
 const AtomicString& SVGElementInstance::interfaceName() const
 {
     return eventNames().interfaceForSVGElementInstance;
 }
 
 ScriptExecutionContext* SVGElementInstance::scriptExecutionContext() const
 {
-    return m_element->document();
+    return &m_element->document();
 }
 
 bool SVGElementInstance::addEventListener(const AtomicString& eventType, PassRefPtr<EventListener> listener, bool useCapture)
 {
     return m_element->addEventListener(eventType, listener, useCapture);
 }
 
 bool SVGElementInstance::removeEventListener(const AtomicString& eventType, EventListener* listener, bool useCapture)
 {
     return m_element->removeEventListener(eventType, listener, useCapture);
@@ skipping 44 matching lines @@
         m_targetElement->setInstanceUpdatesBlocked(true);
 }
 
 SVGElementInstance::InstanceUpdateBlocker::~InstanceUpdateBlocker()
 {
     if (m_targetElement)
         m_targetElement->setInstanceUpdatesBlocked(false);
 }
 
 }