@Override
  public Iterable<FileStatus> getDeletableFiles(Iterable<FileStatus> files) {
    return Iterables.filter(files, this::isFileDeletable);
  }
Base class for file cleaners which allows subclasses to implement a simple isFileDeletable method
(which used to be the FileCleanerDelegate contract).
hbase-server/src/main/java/org/apache/hadoop/hbase/master/cleaner/BaseFileCleanerDelegate.java