dart2js: run dartfmt on tests

tests/compiler/dart2js_extra/16400_test.dart

 // Copyright (c) 2014, 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.
 
 main() {
-  L: {
+  L:
+  {
     var seeMe = 0;
     if (seeMe == 0) {
       ++seeMe;
       break L;
     }
     var wontSeeMe = 2;
     if (seeMe + wontSeeMe == 2) {
       return true;
     } else {
       return false;
     }
   }
 }
-