Bug 126658 [CommonNavigator] [DND] Complete definition of DND API
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
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 WeakHashMap contributionMemory;
	private ITreeContentProvider contentProvider;
	private ILabelProvider labelProvider;
	private final VisibilityAssistant assistant;
	private NavigatorFilterService navigatorFilterService;
	private INavigatorSorterService navigatorSorterService;
	private INavigatorPipelineService navigatorPipelineService;
	private INavigatorDnDService navigatorDnDService;
	private IDescriptionProvider descriptionProvider;
	private boolean contentProviderInitialized;
	private boolean labelProviderInitialized;
	/**
	 * @param aViewerId
	 *            The viewer id for this content service; normally from the
	 *            <b>org.eclipse.ui.views</b> extension.
	 */
	public NavigatorContentService(String aViewerId) {
		super();
		aViewerId = aViewerId != null ? aViewerId : ""; 
		viewerDescriptor = VIEWER_DESCRIPTOR_REGISTRY
				.getNavigatorViewerDescriptor(aViewerId);
		assistant = new VisibilityAssistant(viewerDescriptor);