Revert "Remove Expect from core library."

tests/corelib/reg_exp_has_match_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.
 
-import "package:expect/expect.dart";
-
 // Dart test program for RegExp.hasMatch.
 
 class RegExpHasMatchTest {
   static testMain() {
     Expect.equals(false, new RegExp("bar").hasMatch("foo"));
     Expect.equals(true, new RegExp("bar|foo").hasMatch("foo"));
     Expect.equals(true, new RegExp("o+").hasMatch("foo"));
   }
 }
 
 main() {
   RegExpHasMatchTest.testMain();
 }