@Override
	public void processEvent(PluginEvent event) {
		if (event instanceof ProgramClosedPluginEvent) {
			clear(((ProgramClosedPluginEvent) event).getProgram());
		}
	}
<CODE>NavigationHistoryPlugin</CODE> is used in conjunction with other plugins to cause program
viewer plugins to change their focus to a certain address. As viewer plugins are directed to one
or more addresses it maintains information about where the viewers have been to support ability
for the viewers to go back to a previous "focus" point.

Services Provided: NavigationHistoryService Events Consumed: ProgramLocationPluginEvent,
ProgramPluginEvent Event Produced: HistoryChangePluginEvent Actions: None.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/navigation/NavigationHistoryPlugin.java