Make dart2js unittests async.

tests/compiler/dart2js/interceptor_test.dart

 // Copyright (c) 2013, 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 'dart:async';
+import 'package:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
 import 'compiler_helper.dart';
 
 const String TEST_ONE = r"""
   foo(a) {
     var myVariableName = a.toString();
     print(myVariableName);
     print(myVariableName);
   }
 """;
 
 const String TEST_TWO = r"""
   class A {
     var length;
   }
   foo(a) {
     print([]); // Make sure the array class is instantiated.
     return new A().length + a.length;
   }
 """;
 
 main() {
-  // Check that one-shot interceptors preserve variable names, see
-  // https://code.google.com/p/dart/issues/detail?id=8106.
-  String generated = compile(TEST_ONE, entry: 'foo');
-  Expect.isTrue(generated.contains(new RegExp(r'[$A-Z]+\.toString\$0\(a\)')));
-  Expect.isTrue(generated.contains('myVariableName'));
-
-  // Check that an intercepted getter that does not need to be
-  // intercepted, is turned into a regular getter call or field
-  // access.
-  generated = compile(TEST_TWO, entry: 'foo');
-  Expect.isFalse(generated.contains(r'a.get$length()'));
-  Expect.isTrue(generated.contains(new RegExp(r'[$A-Z]+\.A\$\(\)\.length')));
-  Expect.isTrue(
-      generated.contains(new RegExp(r'[$A-Z]+\.get\$length\$as\(a\)')));
+  asyncTest(() => Future.wait([
+    // Check that one-shot interceptors preserve variable names, see
+    // https://code.google.com/p/dart/issues/detail?id=8106.
+    compile(TEST_ONE, entry: 'foo', check: (String generated) {
+      Expect.isTrue(
+          generated.contains(new RegExp(r'[$A-Z]+\.toString\$0\(a\)')));
+      Expect.isTrue(generated.contains('myVariableName'));
+    }),
+    // Check that an intercepted getter that does not need to be
+    // intercepted, is turned into a regular getter call or field
+    // access.
+    compile(TEST_TWO, entry: 'foo', check: (String generated) {
+      Expect.isFalse(generated.contains(r'a.get$length()'));
+      Expect.isTrue(
+          generated.contains(new RegExp(r'[$A-Z]+\.A\$\(\)\.length')));
+      Expect.isTrue(
+          generated.contains(new RegExp(r'[$A-Z]+\.get\$length\$as\(a\)')));
+    }),
+  ]));
 }