Bug 307747 EPartService doesn't render new parts
1. Have a part in a stack, it is the selected part. 2. Show another part in that stack using PartState.CREATE or PartState.VISIBLE. 3. The part should've been rendered. It is not.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertEquals(partFront, partService.getActivePart());
		PartListener partListener = new PartListener();
		partService.addPartListener(partListener);
		partService.activate(partBack);
		assertEquals(1, partListener.getHidden());
		assertEquals(partFront, partListener.getHiddenParts().get(0));
		assertTrue(partListener.isValid());
		partListener.clear();
		partService.activate(partFront);
		assertEquals(1, partListener.getHidden());
		assertEquals(partBack, partListener.getHiddenParts().get(0));
		assertTrue(partListener.isValid());
	}
	public void testEvent_PartHidden2() {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		MWindow windowA = MApplicationFactory.eINSTANCE.createWindow();
		MWindow windowB = MApplicationFactory.eINSTANCE.createWindow();
		application.getChildren().add(windowA);
		application.getChildren().add(windowB);
		application.setSelectedElement(windowA);
		MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
		windowB.getChildren().add(stack);
		windowB.setSelectedElement(stack);
		MPart partA = MApplicationFactory.eINSTANCE.createPart();
		MPart partB = MApplicationFactory.eINSTANCE.createPart();
		stack.getChildren().add(partA);
		stack.getChildren().add(partB);