Add VM class for Map/LinkedHashMap.

tests/corelib/hash_map2_internal_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.
 
+// This copy of hash_map2_test exercises the internal Map implementation. 
+// VMOptions=--use_internal_hash_map
+
 // Tests of hash map behavior, with focus in iteration and concurrent
 // modification errors.
 
 library hash_map2_test;
 import "package:expect/expect.dart";
 import 'dart:collection';
 
 testMap(Map newMap(), Map newMapFrom(Map map)) {
   Map gen(int from, int to) {
     Map map = new LinkedHashMap();
@@ skipping 266 matching lines @@
   testMap(() => new LinkedHashMap(), (m) => new LinkedHashMap.from(m));
 }
 
 
 class BadHashCode {
   static int idCounter = 0;
   final int id;
   BadHashCode() : id = idCounter++;
   int get hashCode => 42;
 }