it waits for received messages
so basically at this moment as we have a clean environment and no received messages it wait to receive a message.

I'm with you on the new message part. 
as this will always pass if we have at least one received  message.

I can do something like:
```python 
        old_message_count = len(self.marionette.find_elements(*self._received_message_content_locator))
        self.wait_for_condition(lambda m: len(self.marionette.find_elements(*self._received_message_content_locator)) == old_message_count+1)
```