added missing constant

Author: fabpot

src/Symfony/Component/HttpFoundation/Response.php

@@ -67,6 +67,7 @@ class Response
     const HTTP_PRECONDITION_REQUIRED = 428;                                       // RFC6585
     const HTTP_TOO_MANY_REQUESTS = 429;                                           // RFC6585
     const HTTP_REQUEST_HEADER_FIELDS_TOO_LARGE = 431;                             // RFC6585
+    const HTTP_UNAVAILABLE_FOR_LEGAL_REASONS = 451;
     const HTTP_INTERNAL_SERVER_ERROR = 500;
     const HTTP_NOT_IMPLEMENTED = 501;
     const HTTP_BAD_GATEWAY = 502;