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 partBack = (MPart) partStack.getChildren().get(1);
		partBack.setToBeRendered(false);
		partStack.setSelectedElement(partFront);
		window.setSelectedElement(partStack);
		application.setSelectedElement(window);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		assertFalse(partBack.isToBeRendered());
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.bringToTop(partBack);
		assertTrue("Bringing a part to the top should cause it to be rendered",
				partBack.isToBeRendered());
	}
	public void testBringToTop_Bug330508_01() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getChildren().add(partA);
		window.setSelectedElement(partA);
		MPartStack partStack = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(partStack);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partB);
		partStack.setSelectedElement(partB);
		initialize(applicationContext, application);
		getEngine().createGui(window);