Make dart2js unittests async.

tests/compiler/dart2js/code_motion_test.dart

Index: tests/compiler/dart2js/code_motion_test.dart
diff --git a/tests/compiler/dart2js/code_motion_test.dart b/tests/compiler/dart2js/code_motion_test.dart
index e45095a1afcaaee692faf8bc17b32bad69410d8a..ea4036ba65720fa05cab87a3239b86f9b9701995 100644
--- a/tests/compiler/dart2js/code_motion_test.dart
+++ b/tests/compiler/dart2js/code_motion_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"""
@@ -21,9 +22,10 @@ foo(int a, int b, bool param2) {
 """;
 
 main() {
-  String generated = compile(TEST_ONE, entry: 'foo');
-  RegExp regexp = new RegExp('a \\+ b');
-  Iterator matches = regexp.allMatches(generated).iterator;
-  Expect.isTrue(matches.moveNext());
-  Expect.isFalse(matches.moveNext());
+  asyncTest(() => compile(TEST_ONE, entry: 'foo', check: (String generated) {
+    RegExp regexp = new RegExp('a \\+ b');
+    Iterator matches = regexp.allMatches(generated).iterator;
+    Expect.isTrue(matches.moveNext());
+    Expect.isFalse(matches.moveNext());
+  }));
 }