code: void addChronoChangedListener(Consumer<Chronology> listener) {
          if (chronoListeners == null) {
              chronoListeners = new ArrayList<Consumer<Chronology>>();
          }
          chronoListeners.add(listener);
      }
docs: Adds a Consumer<Chronology> to the list of listeners to be notified
  if the Chronology changes.
  @param listener a Consumer<Chronology> to be called when Chronology changes