Make sure getAttribute() / setAttribute() callers use AtomicStrings

Source/core/loader/DocumentLoader.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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.
@@ skipping 87 matching lines @@
 
         const SubstituteData& substituteData() const { return m_substituteData; }
 
         // FIXME: This is the same as requestURL(). We should remove one of them.
         const KURL& url() const;
         const KURL& unreachableURL() const;
         bool isURLValidForNewHistoryEntry() const;
 
         const KURL& originalURL() const;
         const KURL& requestURL() const;
-        const String& responseMIMEType() const;
+        const AtomicString& responseMIMEType() const;
 
         void updateForSameDocumentNavigation(const KURL&);
         void stopLoading();
         void setCommitted(bool committed) { m_committed = committed; }
         bool isCommitted() const { return m_committed; }
         bool isLoading() const;
         const ResourceResponse& response() const { return m_response; }
         const ResourceError& mainDocumentError() const { return m_mainDocumentError; }
         bool isClientRedirect() const { return m_isClientRedirect; }
         void setIsClientRedirect(bool isClientRedirect) { m_isClientRedirect = isClientRedirect; }
@@ skipping 137 matching lines @@
         unsigned long m_identifierForLoadWithoutResourceLoader;
 
         DocumentLoaderTimer m_dataLoadTimer;
 
         friend class ApplicationCacheHost;  // for substitute resource delivery
         OwnPtr<ApplicationCacheHost> m_applicationCacheHost;
     };
 }
 
 #endif // DocumentLoader_h