Use AtomicString type more consistently for mimeType / encoding

Source/core/loader/SubstituteData.h

 /*
  * Copyright (C) 2007 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 19 matching lines @@
 #include "platform/weborigin/KURL.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 
 namespace WebCore {
 
     class SubstituteData {
     public:
         SubstituteData() { }
 
-        SubstituteData(PassRefPtr<SharedBuffer> content, const String& mimeType, const String& textEncoding, const KURL& failingURL)
+        SubstituteData(PassRefPtr<SharedBuffer> content, const AtomicString& mimeType, const AtomicString& textEncoding, const KURL& failingURL)
             : m_content(content)
             , m_mimeType(mimeType)
             , m_textEncoding(textEncoding)
             , m_failingURL(failingURL)
         {
         }
 
         bool isValid() const { return m_content != 0; }
 
         const SharedBuffer* content() const { return m_content.get(); }
-        const String& mimeType() const { return m_mimeType; }
-        const String& textEncoding() const { return m_textEncoding; }
+        const AtomicString& mimeType() const { return m_mimeType; }
+        const AtomicString& textEncoding() const { return m_textEncoding; }
         const KURL& failingURL() const { return m_failingURL; }
 
     private:
         RefPtr<SharedBuffer> m_content;
-        String m_mimeType;
-        String m_textEncoding;
+        AtomicString m_mimeType;
+        AtomicString m_textEncoding;
         KURL m_failingURL;
         KURL m_responseURL;
     };
 
 }
 
 #endif // SubstituteData_h