@Override
	public synchronized void windowHidden(DropDownTextField<T> field) {
		events.add(new WindowShownInfo(field, false));
	}
A spy that tracks window shown and hidden events from the {@link DropDownSelectionTextField}.

<P>Synchronization Policy: the event storage of this class is synchronized to prevent 
concurrent modification exceptions between reading and writing.
Ghidra/Framework/Docking/src/test/java/docking/widgets/SpyDropDownWindowVisibilityListener.java