Fixing iframe.contentWindow.postMessage passing incorrect data

tests/html/postmessage_structured_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
 
 library postmessage_js_test;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_individual_config.dart';
 import 'dart:html';
 import 'dart:collection';  // SplayTreeMap
 import 'dart:typed_data';
@@ skipping 131 matching lines @@
     var view_b = new Uint8List.view(array_buffer, 1, 13);
     var typed_arrays_list = [view_a, array_buffer, view_b];
 
     // Note that FF is failing this test because in the sent message:
     // view_a.buffer == array_buffer
     // But in the response:
     // view_a.buffer != array_buffer
     go('typed_arrays_list', typed_arrays_list);
   });
 
+  group('iframe', () {
+    test('postMessage clones data', () {
+      var iframe = new IFrameElement();
+      var future = iframe.onLoad.first.then((_) {
+        iframe.contentWindow.postMessage(new HashMap<String,num>(), '*');
+      });
+      iframe.src = 'about:blank';
+      document.body.append(iframe);
+
+      return future;
+    });
+  });
+
 }