Revert "Remove Expect from core library."

tests/corelib/for_in_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 ForInTest {
   static testMain() {
     testSimple();
     testBreak();
     testContinue();
     testClosure();
   }
 
   static Set<int> getSmallSet() {
     Set<int> set = new Set<int>();
@@ skipping 71 matching lines @@
     }
 
     Expect.equals(index, set.length);
     Expect.equals(7, closures[0]() + closures[1]() + closures[2]());
   }
 }
 
 main() {
   ForInTest.testMain();
 }