/**
 * Exposed for testing.
 * @param clock the {@link Clock} to use for the {@link CachedGauge}.
 * @param reservoir the {@link Reservoir} to use for the histogram.
 * @param timeoutMs the timeout for the value stored in the cache in milliseconds. After this time has passed, a new
 *                  value of the histogram at {@code quantile} will be calculated.
 * @param quantile the quantile of the histogram to cache.
 */
CachedHistogram(Clock clock, Reservoir reservoir, long timeoutMs, double quantile) {
  super(reservoir);
  cache = new CachedGauge<Double>(clock, timeoutMs, TimeUnit.MILLISECONDS) {
    @Override
    protected Double loadValue() {
      return getSnapshot().getValue(quantile);
    }
  };
}