pkg/unittest: much cleaner support for arbitrary args in expectAsync functions

pkg/unittest/test/unittest_correct_callback_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.
 
 library unittestTest;
 import 'dart:isolate';
 import 'dart:async';
 import 'package:unittest/unittest.dart';
 
 part 'unittest_test_utils.dart';
 
 var testName = 'correct callback test';
 
 var testFunction = (TestConfiguration testConfig) {
   test(testName,
-      () =>_defer(expectAsync0((){ ++testConfig.count;})));
+      () =>_defer(expectAsync((){ ++testConfig.count;})));
 };
 
 var expected = buildStatusString(1, 0, 0, testName, count: 1);