dart2js: run dartfmt on tests

tests/compiler/dart2js/preserve_uris_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.
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'memory_compiler.dart' show runCompiler, OutputCollector;
 
-const MEMORY_SOURCE_FILES = const <String, String> {
+const MEMORY_SOURCE_FILES = const <String, String>{
   'main.dart': """
 library main;
 
 @MirrorsUsed(targets: const ['main', 'lib'])
 import 'dart:mirrors';
 import 'lib.dart';
 
 
 class Subclass extends Super {
   int _private;
@@ skipping 29 matching lines @@
   Expect.equals(preserveUris, jsOutput.contains("main.dart"));
   Expect.equals(preserveUris, jsOutput.contains("lib.dart"));
 }
 
 void main() {
   asyncTest(() async {
     await runTest(true);
     await runTest(false);
   });
 }