Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
private static final String[] NO_EXTENSION_IDS = new String[0];
	private final NavigatorViewerDescriptor viewerDescriptor;
	private final List listeners = new ArrayList();
	/*
	 * A map of (String-based-Navigator-Content-Extension-IDs,
	 * NavigatorContentExtension-objects)-pairs
	 */
	private final Map contentExtensions = new HashMap();
	private StructuredViewerManager structuredViewerManager;
	private ITreeContentProvider[] rootContentProviders;
	private ITreeContentProvider contentProvider;
	/*
	 * Used when providing objects to the CommonViewer by the contentProvider
	 * to record the object/description associations which are when stored
	 * in the Tree associated with the viewer.
	 */
	private Map contributionMemory;
	private Map contributionMemoryFirstClass;
	
	private ILabelProvider labelProvider;
	private final VisibilityAssistant assistant;
	private NavigatorFilterService navigatorFilterService;
	private NavigatorSorterService navigatorSorterService;
	private INavigatorPipelineService navigatorPipelineService;
	private INavigatorDnDService navigatorDnDService;
	private INavigatorActivationService navigatorActivationService;
	private NavigatorSaveablesService navigatorSaveablesService;
	private NavigatorExtensionStateService navigatorExtensionStateService;
	private IDescriptionProvider descriptionProvider;
	private boolean contentProviderInitialized;