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
MPartStack partStack = BasicFactoryImpl.eINSTANCE.createPartStack();
		perspectiveA.getChildren().add(partStack);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partB);
		MPart partC = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partC);
		partStack.setSelectedElement(partC);
		MPerspective perspectiveB = AdvancedFactoryImpl.eINSTANCE
				.createPerspective();
		perspectiveStack.getChildren().add(perspectiveB);
		MPlaceholder areaPlaceholderB = AdvancedFactoryImpl.eINSTANCE
				.createPlaceholder();
		areaPlaceholderB.setRef(area);
		perspectiveB.getChildren().add(areaPlaceholderB);
		perspectiveB.setSelectedElement(areaPlaceholderB);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		partService.switchPerspective(perspectiveB);
		partService.hidePart(partA);
		partService.switchPerspective(perspectiveA);
		assertEquals(partC, partService.getActivePart());
	}
	/**
	 * Setup a shared part in two perspectives, perspectiveA and perspectiveB
	 * with the part being in a detached window in perspectiveB's case.
	 * <p>
	 * First activate the part in perspectiveA. Switching to perspectiveB should
	 * not cause any problems.