Bug 337002 EPartService leaks previously active part
A reference is kept to the previously active part. This is unnecessary. We only need it to fire events. After the deactivation events have been fired, we should no longer need to keep it lying around.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
void postConstruct() {
		eventBroker.subscribe(UIEvents.buildTopic(UIEvents.ElementContainer.TOPIC,
				UIEvents.ElementContainer.SELECTEDELEMENT), selectedHandler);
		constructed = true;
		partActivationHistory = new PartActivationHistory(this, modelService);
		if (activePart != null) {
			partActivationHistory.prepend(activePart);
		}
	}
	@PreDestroy
	void preDestroy() {
		constructed = false;
		eventBroker.unsubscribe(selectedHandler);
		partActivationHistory.clear();
	}
	private void firePartActivated(MPart part) {
		for (Object listener : listeners.getListeners()) {
			((IPartListener) listener).partActivated(part);
		}
	}
	private void firePartDeactivated(MPart part) {
		for (Object listener : listeners.getListeners()) {
			((IPartListener) listener).partDeactivated(part);
		}
	}
	private void firePartHidden(MPart part) {
		for (Object listener : listeners.getListeners()) {
			((IPartListener) listener).partHidden(part);
		}
	}