protected static String timeToString(final TimeUnit timeUnit) {
    switch (timeUnit) {
      case NANOSECONDS:
        return "nsec";
      case MICROSECONDS:
        return "usec";
      case MILLISECONDS:
        return "msec";
      case SECONDS:
        return "sec";
      case MINUTES:
        return "min";
      case HOURS:
        return "hour";
      case DAYS:
        return "day";
    }
    throw new RuntimeException("Invalid TimeUnit " + timeUnit);
  }
Called by toSetQuotaRequestProto() the subclass should implement this method to set the
specific SetQuotaRequest properties.
hbase-client/src/main/java/org/apache/hadoop/hbase/quotas/QuotaSettings.java