Revert "Remove Expect from core library."

tests/standalone/io/secure_no_builtin_roots_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:io";
 import "dart:uri";
 import "dart:isolate";
 import "dart:async";
 
 void testGoogleUrl() {
   ReceivePort keepAlive = new ReceivePort();
   HttpClient client = new HttpClient();
   client.getUrl(Uri.parse('https://www.google.com'))
       .then((request) => request.close())
       .then((response) => Expect.fail("Unexpected successful connection"))
       .catchError((error) {
         Expect.isTrue(error is AsyncError);
         Expect.isTrue(error.error is SocketIOException);
         keepAlive.close();
         client.close();
       });
 }
 
 void InitializeSSL() {
   // If the built-in root certificates aren't loaded, the connection
   // should signal an error.
   SecureSocket.initialize(useBuiltinRoots: false);
 }
 
 void main() {
   InitializeSSL();
   testGoogleUrl();
 }