Bug 126658 [CommonNavigator] [DND] Complete definition of DND API
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
NavigatorActivationService.getInstance()
				.addExtensionActivationListener(viewerDescriptor.getViewerId(),
						this);
	}
	/**
	 * @param aViewerId
	 *            The viewer id for this content service; normally from the
	 *            <b>org.eclipse.ui.views</b> extension.
	 * @param aViewer
	 *            The viewer that this content service will be associated with.
	 */
	public NavigatorContentService(String aViewerId, StructuredViewer aViewer) {
		this(aViewerId);
		structuredViewerManager = new StructuredViewerManager(aViewer);
	}
	public String[] getVisibleExtensionIds() {
		List visibleExtensionIds = new ArrayList();
		NavigatorContentDescriptor[] descriptors = CONTENT_DESCRIPTOR_REGISTRY
				.getAllContentDescriptors();
		for (int i = 0; i < descriptors.length; i++) {
			if (assistant.isVisible(descriptors[i].getId()))
				visibleExtensionIds.add(descriptors[i].getId());
		}
		if (visibleExtensionIds.isEmpty())
			return NO_EXTENSION_IDS;
		return (String[]) visibleExtensionIds
				.toArray(new String[visibleExtensionIds.size()]);
	}
	public INavigatorContentDescriptor[] getVisibleExtensions() {
		List visibleDescriptors = new ArrayList();