Make dart2js unittests async.

tests/compiler/dart2js/literal_list_test.dart

Index: tests/compiler/dart2js/literal_list_test.dart
diff --git a/tests/compiler/dart2js/literal_list_test.dart b/tests/compiler/dart2js/literal_list_test.dart
index efb146d7272d82b3af294930d0e0904aee9495a4..7544f9081668f9af04061e6dd44371ad6b4a4935 100644
--- a/tests/compiler/dart2js/literal_list_test.dart
+++ b/tests/compiler/dart2js/literal_list_test.dart
@@ -2,7 +2,8 @@
 // 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:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
 import 'compiler_helper.dart';
 
 const String TEST_ONE = r"""
@@ -15,8 +16,9 @@ foo() {
 """;
 
 main() {
-  String generated = compile(TEST_ONE, entry: 'foo');
-  Expect.isTrue(generated.contains('print([1, 2]);'));
-  Expect.isTrue(generated.contains('print([3]);'));
-  Expect.isTrue(generated.contains('print([4, 5]);'));
+  asyncTest(() => compile(TEST_ONE, entry: 'foo', check: (String generated) {
+    Expect.isTrue(generated.contains('print([1, 2]);'));
+    Expect.isTrue(generated.contains('print([3]);'));
+    Expect.isTrue(generated.contains('print([4, 5]);'));
+  }));
 }