Determine the current usage for each limit of this service,
        and update corresponding Limit via
        :py:meth:`~.AwsLimit._add_current_usage`.

def find_usage(self):
        """
        Determine the current usage for each limit of this service,
        and update corresponding Limit via
        :py:meth:`~.AwsLimit._add_current_usage`.
        """
        logger.debug("Checking usage for service %s", self.service_name)
        self.connect()
        for lim in self.limits.values():
            lim._reset_usage()
        try:
            self._find_delivery_streams()
        except EndpointConnectionError as ex:
            logger.warning(
                'Caught exception when trying to use Firehose ('
                'perhaps the Firehose service is not available in this '
                'region?): %s', ex
            )

        self._have_usage = True
        logger.debug("Done checking usage.")