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.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
partStack.getChildren().add(partC);
		partStack.setSelectedElement(partC);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		MPart partD = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partD);
		partService.showPart(partD, PartState.ACTIVATE);
		assertEquals(partD, partStack.getSelectedElement());
		assertEquals(partD, partService.getActivePart());
		partService.hidePart(partD);
		assertEquals(partC, partStack.getSelectedElement());
		assertEquals(partA, partService.getActivePart());
	}
	public void testHidePart_ActivationHistory_Bug329482_05() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		MPartSashContainer partSashContainer = BasicFactoryImpl.eINSTANCE
				.createPartSashContainer();
		window.getChildren().add(partSashContainer);
		window.setSelectedElement(partSashContainer);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();