Make dart2js unittests async.

tests/compiler/dart2js/type_inference4_test.dart

Index: tests/compiler/dart2js/type_inference4_test.dart
diff --git a/tests/compiler/dart2js/type_inference4_test.dart b/tests/compiler/dart2js/type_inference4_test.dart
index ace9eee2c91855e29eb7cbb648ae82e5e6ac6196..e8c4180eaa861ff2de69f9cd22fd386b0cbe5c03 100644
--- a/tests/compiler/dart2js/type_inference4_test.dart
+++ b/tests/compiler/dart2js/type_inference4_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"""
@@ -16,13 +17,14 @@ foo(j) {
 """;
 
 main() {
-  String generated = compile(TEST_ONE, entry: 'foo');
+  asyncTest(() => compile(TEST_ONE, entry: 'foo', check: (String generated) {
 
-  // Test for absence of an illegal argument exception. This means that the
-  // arguments are known to be integers.
-  Expect.isFalse(generated.contains('iae'));
-  // Also make sure that we are not just in bailout mode without speculative
-  // types by grepping for the integer-bailout check on argument j.
-  RegExp regexp = new RegExp(getIntTypeCheck('[aji]'));
-  Expect.isTrue(regexp.hasMatch(generated));
+    // Test for absence of an illegal argument exception. This means that the
+    // arguments are known to be integers.
+    Expect.isFalse(generated.contains('iae'));
+    // Also make sure that we are not just in bailout mode without speculative
+    // types by grepping for the integer-bailout check on argument j.
+    RegExp regexp = new RegExp(getIntTypeCheck('[aji]'));
+    Expect.isTrue(regexp.hasMatch(generated));
+  }));
 }