Revert "Remove Expect from core library."

tests/standalone/io/secure_server_client_certificate_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:async";
 import "dart:io";
 import "dart:isolate";
 
 const SERVER_ADDRESS = "127.0.0.1";
 const HOST_NAME = "localhost";
 const CERTIFICATE = "localhost_cert";
 
 void testClientCertificate() {
   ReceivePort port = new ReceivePort();
@@ skipping 103 matching lines @@
   Path certificateDatabase = scriptDir.append('pkcert');
   SecureSocket.initialize(database: certificateDatabase.toNativePath(),
                           password: 'dartdart',
                           useBuiltinRoots: false);
 
   testClientCertificate();
   testRequiredClientCertificate();
   testNoClientCertificate();
   testNoRequiredClientCertificate();
 }