pkg/unittest: support up to 6 arguments in expectAsync[Until]

pkg/unittest/test/unittest_correct_callback_test.dart

Index: pkg/unittest/test/unittest_correct_callback_test.dart
diff --git a/pkg/unittest/test/unittest_correct_callback_test.dart b/pkg/unittest/test/unittest_correct_callback_test.dart
index cd52ba060a13f5f8563b4f7edffcd1a52c6ef491..43b40eab2672f7fea8fc9a5dd61acdba1da52481 100644
--- a/pkg/unittest/test/unittest_correct_callback_test.dart
+++ b/pkg/unittest/test/unittest_correct_callback_test.dart
@@ -13,7 +13,7 @@ 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);