Revert "Remove Expect from core library."

tests/language/deopt_no_feedback_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.
 // Test deoptimization caused by running code that did not collect type
 // feedback before.
 
-import "package:expect/expect.dart";
-
 testStoreIndexed() {
   test(a, i, v, flag) {
     if (flag) {
       // No type feedback in first pass
       return a[i] = v;
     } else {
       return a[i] = i;
     }
   }
 
@@ skipping 27 matching lines @@
   var r = test(10, true);
   Expect.equals(11, r);
 }
 
 
 main() {
   for (var i = 0; i < 2000; i++) {}
   testStoreIndexed();
   testIncrLocal();
 }