@Override
    public MetricRegistry getMetricRegistryForRegionServer() {
      return metricRegistry;
    }
Constructor
@param impl     the coprocessor instance
@param priority chaining priority
@param seq      load sequence
@param conf     configuration
@param wal      WAL
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/WALCoprocessorHost.java