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.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
public boolean isPartVisible(MPart part) {
		if (isInContainer(part)) {
			MUIElement element = part;
			MElementContainer<?> parent = part.getParent();
			if (parent == null) {
				
				element = part.getCurSharedRef();
				if (element == null) {
					return false;
				}
				parent = element.getParent();
				if (parent == null) {
					return false;
				}
			}
			if (parent instanceof MPartStack) {
				return parent.getSelectedElement() == element;
			}
			return element.isVisible();
		}
		return false;
	}
	private boolean isInContainer(MUIElement element) {
		List<MUIElement> allPerspectiveElements = modelService.findElements(workbenchWindow, null,
				MUIElement.class, null, EModelService.PRESENTATION);
		return allPerspectiveElements.contains(element);
	}
	boolean isInContainer(MElementContainer<?> container, MUIElement element) {
		for (Object object : container.getChildren()) {
			if (object == element) {