Revert "Remove Expect from core library."

tests/corelib/reg_exp1_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 RegExp1Test {
   static testMain() {
     RegExp exp1 = new RegExp("bar|foo");
     Expect.equals(true, exp1.hasMatch("foo"));
     Expect.equals(true, exp1.hasMatch("bar"));
     Expect.equals(false, exp1.hasMatch("gim"));
     Expect.equals(true, exp1.hasMatch("just foo"));
     Expect.equals("bar|foo", exp1.pattern);
     Expect.equals(false, exp1.isMultiLine);
     Expect.equals(true, exp1.isCaseSensitive);
 
     RegExp exp2 = new RegExp("o+", caseSensitive: false);
     Expect.equals(true, exp2.hasMatch("this looks good"));
     Expect.equals(true, exp2.hasMatch("fOO"));
     Expect.equals(false, exp2.hasMatch("bar"));
     Expect.equals("o+", exp2.pattern);
     Expect.equals(false, exp2.isCaseSensitive);
     Expect.equals(false, exp2.isMultiLine);
   }
 }
 
 main() {
   RegExp1Test.testMain();
 }