Update HTTPHeaderMap wrappers to use AtomicString type for header values

Source/modules/websockets/WebSocketHandshake.h

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 62 matching lines @@
     // We're collecting data for histogram in the destructor. Note that calling
     // this method affects that.
     void reset();
     void clearExecutionContext();
 
     int readServerHandshake(const char* header, size_t len);
     Mode mode() const;
     // Returns a string indicating the reason of failure if mode() == Failed.
     String failureReason() const;
 
-    String serverWebSocketProtocol() const;
-    String serverSetCookie() const;
-    String serverSetCookie2() const;
-    String serverUpgrade() const;
-    String serverConnection() const;
-    String serverWebSocketAccept() const;
+    const AtomicString& serverWebSocketProtocol() const;
+    const AtomicString& serverSetCookie() const;
+    const AtomicString& serverSetCookie2() const;
+    const AtomicString& serverUpgrade() const;
+    const AtomicString& serverConnection() const;
+    const AtomicString& serverWebSocketAccept() const;
     String acceptedExtensions() const;
 
     const WebSocketHandshakeResponse& serverHandshakeResponse() const;
 
     void addExtensionProcessor(PassOwnPtr<WebSocketExtensionProcessor>);
 
     static String getExpectedWebSocketAccept(const String& secWebSocketKey);
 
 private:
     KURL httpURLForAuthenticationAndCookies() const;
@@ skipping 22 matching lines @@
 
     String m_secWebSocketKey;
     String m_expectedAccept;
 
     WebSocketExtensionDispatcher m_extensionDispatcher;
 };
 
 } // namespace WebCore
 
 #endif // WebSocketHandshake_h