@Override
  public synchronized MetricsMasterQuotaSource create(MetricsMasterWrapper masterWrapper) {
    if (quotaSource == null) {
      quotaSource = new MetricsMasterQuotaSourceImpl(masterWrapper);
    }
    return quotaSource;
  }
Factory to create MetricsMasterQuotaSource instances when given a MetricsMasterWrapper.
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/master/MetricsMasterQuotaSourceFactoryImpl.java