Fix for postMessage on dart2js

lib/dom/frog/dom_frog.dart

Index: lib/dom/frog/dom_frog.dart
diff --git a/lib/dom/frog/dom_frog.dart b/lib/dom/frog/dom_frog.dart
index 6fdffe1b7930b026db544b6724efb0f33afa22a2..594e5350ff17847d123cb92e9e1fd7eb0bd967a8 100644
--- a/lib/dom/frog/dom_frog.dart
+++ b/lib/dom/frog/dom_frog.dart
@@ -24978,12 +24978,23 @@ class _DOMWindowCrossFrameImpl implements DOMType, DOMWindow {
                    String targetOrigin,
                    [List messagePorts = null]) {
     if (messagePorts == null) {
-      _window.postMessage(message, targetOrigin);
+      _postMessage2(_window, message, targetOrigin);
     } else {
-      _window.postMessage(message, targetOrigin, messagePorts);
+      _postMessage3(_window, message, targetOrigin, messagePorts);
     }
   }
 
+  // TODO(vsm): This is a hack to workaround dartbug.com/3175.  We
+  // need a more robust convention to invoke JS methods on the
+  // underlying window.
+  static void _postMessage2(win, message, targetOrigin) native """
+    win.postMessage(message, targetOrigin);
+""";
+
+  static void _postMessage3(win, message, targetOrigin, messagePorts) native """
+    win.postMessage(message, targetOrigin, messagePorts);
+""";
+
   // Implementation support.
   _DOMWindowCrossFrameImpl(this._window);