Bug 263845 [CommonNavigator] Drag/drop folder from non-Java Proj to Java Proj does copy instead of move sometimes
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
*/
    private boolean expandEnabled = true;
    
    /**
     * A flag that allows adapter users to turn selection feedback
     *  on or off. Default is <code>true</code>.
     */
    private boolean selectFeedbackEnabled = true;
    /**
     * Creates a new drop adapter for the given viewer.
     *
     * @param viewer the viewer
     */
    protected ViewerDropAdapter(Viewer viewer) {
        this.viewer = viewer;
    }
    /**
     * Returns the position of the given event's coordinates relative to its target.
     * The position is determined to be before, after, or on the item, based on
     * some threshold value.
     *
     * @param event the event
     * @return one of the <code>LOCATION_* </code>constants defined in this class
     */
    protected int determineLocation(DropTargetEvent event) {
        if (!(event.item instanceof Item)) {
            return LOCATION_NONE;
        }
        Item item = (Item) event.item;
        Point coordinates = new Point(event.x, event.y);