'A user has stopped syncing. We wait before notifying the master as
its likely they\'ll come back soon. This allows us to avoid sending
a stopped syncing immediately followed by a started syncing notification
to the master
Args:
user_id (str)'

def mark_as_going_offline(self, user_id):

    self.users_going_offline[user_id] = self.clock.time_msec()
