* seconds, we can save up to 2 * 10 = 20 permits.
   */
  static final class SmoothBursty extends SmoothRateLimiter {
    /** The work (permits) of how many seconds can be saved up if this RateLimiter is unused? */
    final double maxBurstSeconds;

    SmoothBursty(SleepingStopwatch stopwatch, double maxBurstSeconds) {
      super(stopwatch);
      this.maxBurstSeconds = maxBurstSeconds;