Revert "Remove Expect from core library."

tests/standalone/io/raw_socket_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
-import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 void testArguments() {
   Expect.throws(() => RawServerSocket.bind("127.0.0.1", 65536));
   Expect.throws(() => RawServerSocket.bind("127.0.0.1", -1));
   Expect.throws(() => RawServerSocket.bind("127.0.0.1", 0, -1));
 }
 
@@ skipping 328 matching lines @@
   testSimpleBind();
   testCloseOneEnd("client");
   testCloseOneEnd("server");
   testInvalidBind();
   testSimpleConnect();
   testServerListenAfterConnect();
   testSimpleReadWrite();
   testPauseServerSocket();
   testPauseSocket();
 }