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
partSashContainer.getChildren().add(partA);
		partSashContainer.setSelectedElement(partA);
		MPartStack partStack = BasicFactoryImpl.eINSTANCE.createPartStack();
		partSashContainer.getChildren().add(partStack);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partB);
		MPart partC = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partC);
		partStack.setSelectedElement(partC);
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		MPart partD = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partD);
		partService.showPart(partD, PartState.ACTIVATE);
		assertEquals(partD, partStack.getSelectedElement());
		assertEquals(partD, partService.getActivePart());
		partService.hidePart(partD);
		assertEquals(partC, partStack.getSelectedElement());
		assertEquals(partA, partService.getActivePart());
	}
	public void testHidePart_ActivationHistory_Bug329482_06() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partA);
		MPerspectiveStack perspectiveStack = AdvancedFactoryImpl.eINSTANCE
				.createPerspectiveStack();