@Override
      protected Double loadValue() {
        return getSnapshot().getValue(quantile);
      }
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.
ambry-utils/src/main/java/com/github/ambry/utils/CachedHistogram.java