dart2js: run dartfmt on tests

tests/compiler/dart2js/string_add_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 "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 
 main() {
-  asyncTest(() => compileAll(
-      r'''main() { return "foo" + "bar"; }''').then((code) {
-    Expect.isTrue(!code.contains(r'$add'));
-  }));
+  asyncTest(
+      () => compileAll(r'''main() { return "foo" + "bar"; }''').then((code) {
+            Expect.isTrue(!code.contains(r'$add'));
+          }));
 }