Revert "Remove Expect from core library."

tests/corelib/const_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() {
   testImmutable(const []);
   testImmutable(const [1]);
   testImmutable(const [1, 2]);
 }
 
 void expectUOE(Function f) {
   Expect.throws(f, (e) => e is UnsupportedError);
 }
 
 testImmutable(var list) {
   expectUOE(() { list.removeRange(0, 0); });
   expectUOE(() { list.removeRange(0, 1); });
   expectUOE(() { list.removeRange(-1, 1); });
 }