Revert "Remove Expect from core library."

tests/standalone/io/http_server_early_server_close_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.
 
-import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 class Server {
   static Future<int> start() {
     return HttpServer.bind("127.0.0.1", 0).then((server) {
       server.listen((HttpRequest request) {
             Timer.run(server.close);
           }, onError: (e) {
@@ skipping 20 matching lines @@
           r.close();
         });
   }
 }
 
 main() {
   Server.start().then((port) {
     new Client(port);
   });
 }