More String + elimination in tests

tests/standalone/io/http_server_socket_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class ExpectedDataOutputStream implements OutputStream {
   ExpectedDataOutputStream(List<int> this._data,
                            int this._cutoff,
@@ skipping 190 matching lines @@
       // TODO(ajohnsen): Validate HttpServers number of connections.
     }
     for (int i = 1; i < response.length; i++) {
       bool _expectError = expectError && i < response.length - okayFrom;
       runSettings(i, false, _expectError);
       runSettings(i, true, _expectError);
     }
   }
   testContent(
       "GET / HTTP/1.1\r\nKeep-Alive: False\r\n\r\n",
-      "HTTP/1.1 200 OK\r\ntransfer-encoding: chunked\r\nconnection: close" +
+      "HTTP/1.1 200 OK\r\ntransfer-encoding: chunked\r\nconnection: close"
       "\r\n\r\n0\r\n\r\n");
 
   server.close();
 }
 
 void main() {
   testSocketClose();
 }