@Override
    public InternalScanner preFlush(ObserverContext<? extends RegionCoprocessorEnvironment> c,
      Store store, InternalScanner scanner, FlushLifeCycleTracker tracker) throws IOException {
      if (TRACKER != null) {
        assertSame(tracker, TRACKER);
      }
      return scanner;
    }
Confirm that the function of FlushLifeCycleTracker is OK as we do not use it in our own code.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestFlushLifeCycleTracker.java