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 partB2 = BasicFactoryImpl.eINSTANCE.createPart();
		stackB.getChildren().add(partB2);
		MPart partB3 = BasicFactoryImpl.eINSTANCE.createPart();
		stackB.getChildren().add(partB3);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partB2);
		partService.activate(partB3);
		partService.activate(partA);
		partService.hidePart(partB3);
		assertEquals(partB2, stackB.getSelectedElement());
	}
	public void testHidePart_ActivationHistory02() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartStack stackA = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(stackA);
		window.setSelectedElement(stackA);
		MPartStack stackB = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(stackB);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		stackA.getChildren().add(partA);
		stackA.setSelectedElement(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		stackB.getChildren().add(partB);
		stackB.setSelectedElement(partB);