Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
* <b>possibleChildren</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @param toLoadIfNecessary
	 *            True will force the load of the extension, False will not
	 * @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>possibleChildren</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findContentExtensionsWithPossibleChild(Object anElement,
			boolean toLoadIfNecessary) {
		Set enabledDescriptors = findDescriptorsWithPossibleChild(anElement);
		return extractDescriptorInstances(enabledDescriptors, toLoadIfNecessary);
	}
	/**
	 * 
	 * 
	 * @param firstClassSource
	 * @param source
	 * @param element
	 */
	public void rememberContribution(INavigatorContentDescriptor source,
			INavigatorContentDescriptor firstClassSource, Object element) {
		/*
		 * We want to write to (overwrite) the contributionMemory only if we
		 * have never heard of the element before, or if the element is coming
		 * from the same first class NCE, which means that the subsequent NCE is
		 * an override. The override will take precedence over the originally