Migrate block 115.

tests/language_2/hash_map_null_key_foreach_test.dart

 // Copyright (c) 2013, 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";
 
 // Regression test for using `null` as a key with `forEach`.
 
 main() {
   var x = new Map<int, int>();
   x[1] = 2;
   x[null] = 1;
   int c = 0;
   x.forEach((int i, int j) {
     c++;
     Expect.isTrue(i == null || i is int, 'int or null expected');
   });
   Expect.equals(2, c);
 }