Does the actual queuing.

def _MultiNotifyQueue(self, queue, notifications, mutation_pool=None):
    """Does the actual queuing."""
    notification_list = []
    now = rdfvalue.RDFDatetime.Now()
    for notification in notifications:
      if not notification.first_queued:
        notification.first_queued = (
            self.frozen_timestamp or rdfvalue.RDFDatetime.Now())
      else:
        diff = now - notification.first_queued
        if diff.seconds >= self.notification_expiry_time:
          # This notification has been around for too long, we drop it.
          logging.debug("Dropping notification: %s", str(notification))
          continue

      notification_list.append(notification)

    mutation_pool.CreateNotifications(
        self.GetNotificationShard(queue), notification_list)