code: public LookupCacheStats plus(LookupCacheStats other)
    {
      return new LookupCacheStats(
          hitCount + other.hitCount,
          missCount + other.missCount,
          evictionCount + other.evictionCount
      );
    }
docs: Returns a new {@code CacheStats} representing the sum of this {@code CacheStats}
  and {@code other}.