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
MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partB);
		MPart partC = BasicFactoryImpl.eINSTANCE.createPart();
		perspective.getChildren().add(partC);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		partService.activate(partC);
		assertEquals(partC, partService.getActivePart());
		partService.bringToTop(partB);
		assertEquals(
				"Bringing a part to top that's not in the same container as the active part shouldn't change the active part",
				partC, partService.getActivePart());
	}
	public void testGetParts_Empty() {
		MApplication application = createApplication(1, new String[1][0]);
		MWindow window = application.getChildren().get(0);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		Collection<MPart> parts = partService.getParts();
		assertNotNull(parts);
		assertEquals(0, parts.size());
	}
	public void testGetParts_OneWindow() {
		MApplication application = createApplication("partId", "partId2");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);