Revert "Remove Expect from core library."

tests/standalone/io/http_connection_info_test.dart

 // Copyright (c) 2013, 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:io";
 
 void testHttpConnectionInfo() {
   HttpServer.bind("0.0.0.0", 0).then((server) {
     int clientPort;
 
     server.listen((request) {
       var response = request.response;
       Expect.isTrue(request.connectionInfo.remoteHost is String);
       Expect.isTrue(response.connectionInfo.remoteHost is String);
@@ skipping 24 matching lines @@
                   client.close();
                   server.close();
                 });
         });
     });
 }
 
 void main() {
   testHttpConnectionInfo();
 }