default WALFileLengthProvider getWALFileLengthProvider() {
    return path -> getWALs().stream().map(w -> w.getLogFileSizeIfBeingWritten(path))
      .filter(o -> o.isPresent()).findAny().orElse(OptionalLong.empty());
  }
Add a {@link WALActionsListener}.
<p>
Notice that you must call this method before calling {@link #getWAL(RegionInfo)} as this method
will not effect the {@link WAL} which has already been created. And as long as we can only it
when initialization, it is not thread safe.
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALProvider.java