@Override
    public MetricsRecordBuilder addRecord(String arg0) {
      MockRecord tr = new MockRecord(arg0);
      records.add(tr);
      return new MockMetricsRecordBuilder(tr);
    }
Used by outer class to provide a new <code>MetricsRecordBuilder</code>
for a single metrics record.

@param t The record to build.
llap-common/src/test/org/apache/hadoop/hive/llap/metrics/TestReadWriteLockMetrics.java