Implement getRange (returning an Iterable).

tests/corelib/list_sublist_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() {
   Expect.listEquals([], [].sublist(0, 0));
   Expect.listEquals([], const [].sublist(0, 0));
 
@@ skipping 38 matching lines @@
   expectAE(() => const [].sublist(1, 1));
 
   expectAE(() => [1].sublist(0, 2));
   expectAE(() => [1].sublist(1, 2));
   expectAE(() => [1].sublist(1, 0));
 }
 
 void expectAE(Function f) {
   Expect.throws(f, (e) => e is ArgumentError);
 }