Revert "Remove Expect from core library."

tests/language/interceptor2_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";
-
 // Regression test for issue http://dartbug.com/6903: dart2js used to
 // not generate an interceptor forwarder when a getter call and a
 // method call on an intercepted method were both used.
 
 class A { get iterator => () => 499; }
 
 main() {
   var a = [new A(), [1, 1]];
   Expect.equals(499, a[0].iterator());
   Expect.equals(499, (a[0].iterator)());
   for (var i in a[1]) {
     Expect.equals(1, i);
   }
 }