Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
*/
	public Set findOverrideableContentExtensionsForPossibleChild(
			Object anElement) {
		Set overrideableExtensions = new TreeSet(
				ExtensionSequenceNumberComparator.INSTANCE);
		Set descriptors = findDescriptorsWithPossibleChild(anElement, false);
		for (Iterator iter = descriptors.iterator(); iter.hasNext();) {
			INavigatorContentDescriptor descriptor = (INavigatorContentDescriptor) iter
					.next();
			if (descriptor.hasOverridingExtensions()) {
				overrideableExtensions.add(getExtension(descriptor));
			}
		}
		return overrideableExtensions;
	}
	/*
	 * (Non-Javadoc)
	 * 
	 * @see INavigatorContentService#getContentDescriptorById(String)
	 */
	public INavigatorContentDescriptor getContentDescriptorById(
			String anExtensionId) {
		return CONTENT_DESCRIPTOR_REGISTRY.getContentDescriptor(anExtensionId);
	}
	/**
	 * 
	 * @param anExtensionId
	 *            The id used to define the
	 *            <b>org.eclipse.ui.navigator.navigatorContent
	 *            /navigatorContent</b> extension.