@Override
	public void addChangeListener(Runnable l) {
		changeListeners.add(l);
	}
NB: This is also the syncing object for the viewport. If there's even a chance an operation
may need the DB's lock, esp., considering user callbacks, then it must <em>first</em> acquire
the DB lock.
Ghidra/Debug/Framework-TraceModeling/src/main/java/ghidra/trace/database/DBTraceTimeViewport.java