Make message listener API backwards compatible.

src/messages.cc

Index: src/messages.cc
diff --git a/src/messages.cc b/src/messages.cc
index 801930d2b3f4b86b2dacb9b5ffe2ef3b5b6c6560..7b0a4d41a40cbbffab0d1ae79efbcb90ea1add74 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -132,13 +132,17 @@ void MessageHandler::ReportMessage(Isolate* isolate,
     for (int i = 0; i < global_length; i++) {
       HandleScope scope;
       if (global_listeners.get(i)->IsUndefined()) continue;
-      Handle<Foreign> callback_obj(Foreign::cast(global_listeners.get(i)));
+      v8::NeanderObject listener(JSObject::cast(global_listeners.get(i)));
+      Handle<Foreign> callback_obj(Foreign::cast(listener.get(0)));
       v8::MessageCallback callback =
           FUNCTION_CAST<v8::MessageCallback>(callback_obj->foreign_address());
+      Handle<Object> callback_data(listener.get(1));
       {
         // Do not allow exceptions to propagate.
         v8::TryCatch try_catch;
-        callback(api_message_obj, api_exception_obj);
+        callback(api_message_obj, callback_data->IsUndefined()
+                                      ? api_exception_obj
+                                      : v8::Utils::ToLocal(callback_data));
       }
       if (isolate->has_scheduled_exception()) {
         isolate->clear_scheduled_exception();