Make Element::elementData() / ensureUniqueElementData() protected

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 52 matching lines @@
 }
 
 const SpaceSplitString& ClassList::classNames() const
 {
     ASSERT(m_element->hasClass());
     if (m_element->document().inQuirksMode()) {
         if (!m_classNamesForQuirksMode)
             m_classNamesForQuirksMode = adoptPtr(new SpaceSplitString(value(), false));
         return *m_classNamesForQuirksMode.get();
     }
-    return m_element->elementData()->classNames();
+    return m_element->classNames();
 }
 
 void ClassList::trace(Visitor* visitor)
 {
     visitor->trace(m_element);
     DOMTokenList::trace(visitor);
 }
 
 } // namespace blink