@Override
  public void close() {
    super.close();
    try {
      this.freeAllReferencedMobCells();
    } catch (IOException e) {
      LOG.warn("Failed to free referenced mob cells: ", e);
    }
  }
Firstly reads the cells from the HBase. If the cell are a reference cell (which has the
reference tag), the scanner need seek this cell from the mob file, and use the cell found from
the mob file as the result.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MobStoreScanner.java