@Override
      public Boolean call(RegionObserver observer) throws IOException {
        return observer.postScannerFilterRow(this, s, curRowCell, getResult());
      }
This will be called by the scan flow when the current scanned row is being filtered out by the
filter.
@param s          the scanner
@param curRowCell The cell in the current row which got filtered out
@return whether more rows are available for the scanner or not
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionCoprocessorHost.java