Bug 79916 [Viewers] isDisposed check needed in AbstractTreeViewer#internalRemove
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* 
     * @return non-negative level, or <code>ALL_LEVELS</code> if all levels
     *         of the tree are expanded automatically
     * @see #setAutoExpandLevel
     */
    public int getAutoExpandLevel() {
        return expandToLevel;
    }
    /**
     * Returns the SWT child items for the given SWT widget.
     * 
     * @param widget
     *           the widget
     * @return the child items
     */
    protected abstract Item[] getChildren(Widget widget);
    /**
     * Returns whether the given SWT item is expanded or collapsed.
     * 
     * @param item
     *           the item
     * @return <code>true</code> if the item is considered expanded and
     *         <code>false</code> if collapsed
     */
    protected abstract boolean getExpanded(Item item);
    /**
     * Returns a list of elements corresponding to expanded nodes in this
     * viewer's tree, including currently hidden ones that are marked as
     * expanded but are under a collapsed ancestor.
     * <p>