protected void setTableRecordReader(TableRecordReader tableRecordReader) {
    this.tableRecordReader = tableRecordReader;
  }
Allows subclasses to set the {@link TableRecordReader}.
@param tableRecordReader A different {@link TableRecordReader} implementation.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/MultiTableInputFormatBase.java