Remove Expect from core library.

tests/standalone/io/string_stream_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:isolate";
 
 void testUtf8() {
   List<int> data = [0x01,
                     0x7f,
                     0xc2, 0x80,
                     0xdf, 0xbf,
                     0xe0, 0xa0, 0x80,
                     0xef, 0xbf, 0xbf,
@@ skipping 311 matching lines @@
   testUtf8();
   testLatin1();
   testAscii();
   testReadLine1();
   testReadLine2();
   testReadChunks();
   testReadMixed();
   testErrorHandler();
   testEncodingErrorWithHandler();
 }