Don't assume that I can use package:-url in test.

tests/lib/async/stream_controller_async_test.dart

Index: tests/lib/async/stream_controller_async_test.dart
diff --git a/tests/lib/async/stream_controller_async_test.dart b/tests/lib/async/stream_controller_async_test.dart
index 262058255581525d125c698002803df75d85b684..0cae4fafd237831af50d8715c27d4744920f0028 100644
--- a/tests/lib/async/stream_controller_async_test.dart
+++ b/tests/lib/async/stream_controller_async_test.dart
@@ -5,10 +5,10 @@
 // Test the basic StreamController and StreamController.singleSubscription.
 library stream_controller_async_test;
 
-import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
-import 'package:unittest/unittest.dart';
+import "package:expect/expect.dart";
+import '../../../pkg/unittest/lib/unittest.dart';
 import 'event_helper.dart';
 import 'stream_state_helper.dart';