Revert "Remove Expect from core library."

tests/language/reg_exp2_test.dart

 // Copyright (c) 2011, 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.
 // Dart test for testing regular expressions in Dart.
 
-import "package:expect/expect.dart";
-
 class RegExp2Test {
   static String findImageTag_(String text, String extensions) {
     final re = new RegExp('src="(http://\\S+\\.(${extensions}))"');
     print('REGEXP findImageTag_ $extensions text: \n$text');
     final match = re.firstMatch(text);
     print('REGEXP findImageTag_ $extensions SUCCESS');
     if (match != null) {
       return match[1];
     } else {
       return null;
     }
   }
 
 
   static testMain() {
     String text = '''<img src="http://cdn.archinect.net/images/514x/c0/c0p3qo202oxp0e6z.jpg" width="514" height="616" border="0" title="" alt=""><em><p>My last entry was in December of 2009. I suppose I never was particularly good about updating this thing, but it seems a bit ridiculous that I couldn't be bothered to post once about the many, many things that have gone on since then. My apologies. I guess I could start by saying that the world looks like a very different place than it did back in second year.</p></em>
 
 ''';
    String extensions = 'jpg|jpeg|png';
    String tag = findImageTag_(text, extensions);
    Expect.isNotNull(tag);
  }
 }
 
 main() {
   RegExp2Test.testMain();
 }