Revert "Remove Expect from core library."

tests/utils/json_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.
 
 library jsonTest;
 
-import "package:expect/expect.dart";
 import 'dart:json';
 
 main() {
   testEscaping();
   testParse();
   testParseInvalid();
 }
 
 void testParse() {
   // Scalars.
@@ skipping 151 matching lines @@
   Expect.stringEquals('"\\u001d"', stringify('\u001d'));
   Expect.stringEquals('"\\u001e"', stringify('\u001e'));
   Expect.stringEquals('"\\u001f"', stringify('\u001f'));
   Expect.stringEquals('"\\\""', stringify('"'));
   Expect.stringEquals('"\\\\"', stringify('\\'));
   Expect.stringEquals('"Got \\b, \\f, \\n, \\r, \\t, \\u0000, \\\\, and \\"."',
       stringify('Got \b, \f, \n, \r, \t, \u0000, \\, and ".'));
   Expect.stringEquals('"Got \\b\\f\\n\\r\\t\\u0000\\\\\\"."',
     stringify('Got \b\f\n\r\t\u0000\\".'));
 }