Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/getter_element_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";
-
 class A {
   static main() {
     testOther();
     new A().testSelf();
   }
 
   static testOther() {
     var o = new A();
     o.instf = 0;
     o.instf += 1;
     Expect.equals(1, o.instf);
   }
 
   testSelf() {
     instf = 0;
     instf += 1;
     Expect.equals(1, instf);
   }
 
   var instf;
 }
 
 main() {
   A.main();
 }