code: public void record(long timeNano, int numEvents) {
      long leftEndPoint = bucket(timeNano);
      mSeries.put(leftEndPoint, mSeries.getOrDefault(leftEndPoint, 0) + numEvents);
    }
docs: Record events at a timestamp into the time series.
  @param timeNano the time in nano seconds
  @param numEvents the number of events happened at timeNano