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
partService.activate(partA);
		partService.activate(partC);
		partService.activate(partB);
		partService.activate(partA);
		partService.switchPerspective(perspectiveB);
		assertEquals(partA, partService.getActivePart());
		partService.hidePart(partA);
		assertEquals(partC, partService.getActivePart());
	}
	/**
	 * Create a window with three parts, partA, partB contained within a part
	 * stack, and partC.
	 * <p>
	 * partA is initially active and then we proceed to activate partB and
	 * partC. Now we turn off the 'toBeRendered' flag of the part stack
	 * containing partB and then hide partC. partA should now become the active
	 * part as partB's parent container has been unrendered despite the fact
	 * that partB is the next available candidate in the activation history.
	 * </p>
	 */
	public void testHidePart_ActivationHistory24() {
		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();