Revert "Remove Expect from core library."

tests/lib/async/futures_test.dart

 // Copyright (c) 2011, 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 futures_test;
-import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
 
 Future testWaitEmpty() {
   List<Future> futures = new List<Future>();
   return Future.wait(futures);
 }
 
 Future testCompleteAfterWait() {
   List<Future> futures = new List<Future>();
@@ skipping 98 matching lines @@
   futures.add(testForEachWithException());
 
   // Use a receive port for blocking the test.
   // Note that if the test fails, the program will not end.
   ReceivePort port = new ReceivePort();
   Future.wait(futures).then((List list) {
     Expect.equals(9, list.length);
     port.close();
   });
 }