Revert "Remove Expect from core library."

tests/language/closure_shared_state_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";
-
 // Tests for closures sharing mutable bindings.
 
 var f;
 var g;
 
 setupPlain() {
   int j = 1000;
   // Two closures sharing variable 'j'; j initially is 1000.
   f = (int x) { var q = j; j = x; return q;};
   g = (int x) { var q = j; j = x; return q;};
@@ skipping 27 matching lines @@
   Expect.equals(300, g(400));
   Expect.equals(400, g(500));
 }
 
 
 main() {
   test(setupPlain);
   test(setupLoop);
   test(setupNestedLoop);
 }