Revert "Remove Expect from core library."

tests/isolate/stream_mangling_test.dart

 // Copyright (c) 2012, 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 stream_mangling_test;
 
-import "package:expect/expect.dart";
 import 'dart:isolate';
 import '../../pkg/unittest/lib/unittest.dart';
 
 main() {
   test("Self referencing arrays serialize correctly", () {
     var messageBox = new MessageBox();
     var stream = messageBox.stream;
     var sink = messageBox.sink;
     var nested = [];
     nested.add(nested);
@@ skipping 76 matching lines @@
   });
 
   test("Sending of IsolateSinks", () {
     // TODO(floitsch): add test.
   });
 
   test("Sending of IsolateSinks in complicated structures", () {
     // TODO(floitsch): add test.
   });
 }