mshtml: Implement `data` getter for MessageEvent objs.

dlls/mshtml/htmlevent.c

@@ -1831,11 +1831,19 @@ static HRESULT WINAPI HTMLEventObj5_put_data(IHTMLEventObj5 *iface, BSTR v)
 static HRESULT WINAPI HTMLEventObj5_get_data(IHTMLEventObj5 *iface, BSTR *p)
 {
     HTMLEventObj *This = impl_from_IHTMLEventObj5(iface);
+    IDOMMessageEvent *message_event;
+    HRESULT hres;
 
-    FIXME("(%p)->(%p)\n", This, p);
+    TRACE("(%p)->(%p)\n", This, p);
 
+    if(!This->event || FAILED(IDOMEvent_QueryInterface(&This->event->IDOMEvent_iface, &IID_IDOMMessageEvent, (void**)&message_event))) {
         *p = NULL;
         return S_OK;
+    }
+
+    hres = IDOMMessageEvent_get_data(message_event, p);
+    IDOMMessageEvent_Release(message_event);
+    return hres;
 }
 
 static HRESULT WINAPI HTMLEventObj5_get_source(IHTMLEventObj5 *iface, IDispatch **p)

dlls/mshtml/tests/events.c

@@ -1537,6 +1537,11 @@ static HRESULT WINAPI onmessage(IDispatchEx *iface, DISPID id, LCID lcid, WORD w
         ok(hres == S_OK, "get_url failed: %08lx\n", hres);
         ok(!bstr, "url = %s\n", wine_dbgstr_w(bstr));
 
+        hres = IHTMLEventObj5_get_data(event_obj5, &bstr);
+        ok(hres == S_OK, "get_data failed: %08lx\n", hres);
+        ok(!wcscmp(bstr, L"foobar"), "data = %s\n", wine_dbgstr_w(bstr));
+        SysFreeString(bstr);
+
         hres = IHTMLEventObj5_get_source(event_obj5, &disp);
         ok(hres == S_OK, "get_source failed: %08lx\n", hres);