Consistently use AtomicString for namespaceURI / prefix

Source/core/xml/XPathNSResolver.h

 /*
  * Copyright 2005 Frerich Raabe <raabe@kde.org>
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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.
@@ skipping 18 matching lines @@
 
 #include "bindings/v8/ScriptWrappable.h"
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 
 namespace WebCore {
 
 class XPathNSResolver : public RefCounted<XPathNSResolver>, public ScriptWrappable {
 public:
     virtual ~XPathNSResolver();
-    virtual String lookupNamespaceURI(const String& prefix) = 0;
+    virtual AtomicString lookupNamespaceURI(const String& prefix) = 0;
 
 protected:
     XPathNSResolver()
     {
         ScriptWrappable::init(this);
     }
 };
 
 }
 
 #endif // XPathNSResolver_h