@Override
  public int getTotalCellsCount() {
    return totalCellsCount;
  }
Clone the cell refs so they can be cleaned up by {@link Shipper#shipped()}. Doing this lazily
here, rather than eagerly in the above two methods can save us on some allocations. We might
change the largestCell/largestRow multiple times between shipped() calls.
hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example/row/stats/RowStatisticsImpl.java