dart2js: run dartfmt on tests

tests/compiler/dart2js/compile_with_empty_libraries_test.dart

 // Copyright (c) 2015, 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.
 
 /// Test that the dart2js compiler can compile an empty script without
 /// references to core library definitions.
 
 import 'package:async_helper/async_helper.dart';
 import 'mock_compiler.dart';
 
 const String TEST = r"main() {}";
 
 main() {
   Uri uri = new Uri(scheme: 'source');
   MockCompiler compiler =
-    new MockCompiler.internal(librariesOverride: (_) => '');
+      new MockCompiler.internal(librariesOverride: (_) => '');
   asyncTest(() => compiler.run(uri));
 }