public static ExtendedCell createMobRefCell(ExtendedCell cell, byte[] fileName,
    byte[] refCellTags) {
    byte[] refValue = Bytes.add(Bytes.toBytes(cell.getValueLength()), fileName);
    return PrivateCellUtil.createCell(cell, refValue, TagUtil.concatTags(refCellTags, cell));
  }
Creates a mob reference KeyValue. The value of the mob reference KeyValue is mobCellValueSize +
mobFileName.
@param cell         The original Cell.
@param fileName     The mob file name where the mob reference KeyValue is written.
@param tableNameTag The tag of the current table name. It's very important in cloning the
                    snapshot.
@return The mob reference KeyValue.
hbase-server/src/main/java/org/apache/hadoop/hbase/mob/MobUtils.java