Migrate test block 11 to Dart 2.0.

tests/corelib_2/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);
 }