Make dart2js unittests async.

tests/compiler/dart2js/identity_test.dart

Index: tests/compiler/dart2js/identity_test.dart
diff --git a/tests/compiler/dart2js/identity_test.dart b/tests/compiler/dart2js/identity_test.dart
index eec4136a8762a46457f88514fca2ddc05967d998..6e25ea483c4512a8f23a60a39236f573f50b22c3 100644
--- a/tests/compiler/dart2js/identity_test.dart
+++ b/tests/compiler/dart2js/identity_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"""
@@ -15,15 +16,16 @@ bool foo(bar) {
 """;
 
 main() {
-  String generated = compile(TEST_ONE, entry: 'foo');
+  asyncTest(() => compile(TEST_ONE, entry: 'foo', check: (String generated) {
 
-  // Check that no boolify code is generated.
-  RegExp regexp = new RegExp("=== true");
-  Iterator matches = regexp.allMatches(generated).iterator;
-  Expect.isFalse(matches.moveNext());
+    // Check that no boolify code is generated.
+    RegExp regexp = new RegExp("=== true");
+    Iterator matches = regexp.allMatches(generated).iterator;
+    Expect.isFalse(matches.moveNext());
 
-  regexp = new RegExp("===");
-  matches = regexp.allMatches(generated).iterator;
-  Expect.isTrue(matches.moveNext());
-  Expect.isFalse(matches.moveNext());
+    regexp = new RegExp("===");
+    matches = regexp.allMatches(generated).iterator;
+    Expect.isTrue(matches.moveNext());
+    Expect.isFalse(matches.moveNext());
+  }));
 }