Sets a theme for posting messages.
            Themes: ["flat", "future", "block", "air", "ice"]
            Locations: ["top_left", "top_center", "top_right",
                        "bottom_left", "bottom_center", "bottom_right"]
            max_messages is the limit of concurrent messages to display.

def set_messenger_theme(self, theme="default", location="default",
                            max_messages="default"):
        """ Sets a theme for posting messages.
            Themes: ["flat", "future", "block", "air", "ice"]
            Locations: ["top_left", "top_center", "top_right",
                        "bottom_left", "bottom_center", "bottom_right"]
            max_messages is the limit of concurrent messages to display. """
        if not theme:
            theme = "default"  # "future"
        if not location:
            location = "default"  # "bottom_right"
        if not max_messages:
            max_messages = "default"  # "8"
        js_utils.set_messenger_theme(
            self.driver, theme=theme,
            location=location, max_messages=max_messages)