Revert "Remove Expect from core library."

tests/corelib/list_remove_range_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";
-
 main() {
   var list = [];
   list.removeRange(0, 0);
   Expect.equals(0, list.length);
   expectIOORE(() { list.removeRange(0, 1); });
 
   list.add(1);
   list.removeRange(0, 0);
   Expect.equals(1, list.length);
   Expect.equals(1, list[0]);
@@ skipping 42 matching lines @@
       (e) => e is ArgumentError);
   Expect.listEquals([1, 2], list);
 
   // A zero length prevails, and does not throw an exception.
   list.removeRange(-1, 0);
   Expect.listEquals([1, 2], list);
 
   list.removeRange(4, 0);
   Expect.listEquals([1, 2], list);
 }