private void notifyHistoryChange() {
		/*
		 * During tool disposal, Plugins having providers that extend
		 * NavigatableComponentProviderAdapter may get disposed after we do. Those providers remove
		 * themselves from us via NavigatableRemovalListener, which eventually calls into here. If
		 * that is the case, our tool will already be set to null, so we'll just ignore the event.
		 */
		if (tool != null) {
			tool.contextChanged(null);
		}
	}
<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