ns the contribution of the given task to expected queueing time
   * in the given time window.
   *
   * The result is probabilityOf(task) * expectedQueueTimeDueTo(task),
   * where
   * - probabilityOf(task) = probability of input arriving while the given
   *   task is running.
   * - expectedQueueingTimeDueTo(task) = expected time until the end of the
   *   given task for input arriving while the task is running.
   *
   * We assume that input arrival time is uniformly distributed in the given
   * time