Bug 135971 [CommonNavigator] Project Explorer: cannot drop to Hierarchy view
You can drag and drop an element onto the Hierarchy view from the Outline or Package Explorer. You cannot from the Project Explorer, you get a drop disabled cursor.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewer.java
* @param aParent
	 *            A Composite parent to contain the actual SWT widget
	 * @param aStyle
	 *            A style mask that will be used to create the TreeViewer
	 *            Composite.
	 */
	public CommonViewer(String aViewerId, Composite aParent, int aStyle) {
		super(aParent, aStyle);
		contentService = new NavigatorContentService(aViewerId, this);
		init();
	}
	/**
	 * <p>
	 * Initializes the content provider, label provider, and drag and drop
	 * support. Should not be called by clients -- this method is invoked when
	 * the constructor is invoked.
	 * </p>
	 */
	protected void init() {
		setUseHashlookup(true);
		setContentProvider(contentService.createCommonContentProvider());
		setLabelProvider(new NavigatorDecoratingLabelProvider(contentService.createCommonLabelProvider()));
		initDragAndDrop();
	}
	void setCommonNavigator(CommonNavigator navigator) {
		commonNavigator = navigator;
	}
	
	/**
	 * @return the CommonNavigator