Remove Expect from core library.

tests/standalone/io/secure_socket_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // The --short_socket_write option does not work with external server
 // www.google.dk.  Add this to the test when we have secure server sockets.
 // See TODO below.
 
+import "package:expect/expect.dart";
 import "dart:isolate";
 import "dart:io";
 
 void WriteAndClose(Socket socket, String message) {
   var data = message.charCodes;
   int written = 0;
   void write() {
     written += socket.writeList(data, written, data.length - written);
     if (written < data.length) {
       socket.onWrite = write;
@@ skipping 30 matching lines @@
     chunks.add(received);
     secure.onData = useRead;
   };
   secure.onData = useRead;
   secure.onClosed = () {
     String fullPage = Strings.concatAll(chunks);
     Expect.isTrue(fullPage.contains('</body></html>'));
     keepAlive.close();
   };
 }