Remove AtomicStringImpl.

Source/core/editing/SetNodeAttributeCommand.cpp

 /*
  * Copyright (C) 2005, 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
 
 void SetNodeAttributeCommand::doApply()
 {
     m_oldValue = m_element->getAttribute(m_attribute);
     m_element->setAttribute(m_attribute, m_value);
 }
 
 void SetNodeAttributeCommand::doUnapply()
 {
     m_element->setAttribute(m_attribute, m_oldValue);
-    AtomicStringImpl* nullString = 0;
+    StringImpl* nullString = 0;
     m_oldValue = nullString;
 }
 
 #ifndef NDEBUG
 void SetNodeAttributeCommand::getNodesInCommand(HashSet<Node*>& nodes)
 {
     addNodeAndDescendants(m_element.get(), nodes);
 }
 #endif
 
 } // namespace WebCore