Migrate test block 11 to Dart 2.0.

tests/corelib/iterable_last_test.dart

-// Copyright (c) 2012, 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() {
-  List<int> list1 = <int>[1, 2, 3];
-  List<int> list2 = const <int>[4, 5];
-  List<String> list3 = <String>[];
-  Set<int> set1 = new Set<int>();
-  set1..add(11)..add(12)..add(13);
-  Set set2 = new Set();
-
-  Expect.equals(3, list1.last);
-  Expect.equals(5, list2.last);
-  Expect.throws(() => list3.last, (e) => e is StateError);
-
-  Expect.isTrue(set1.contains(set1.last));
-
-  Expect.throws(() => set2.last, (e) => e is StateError);
-}