Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* @return <code>true</code> if the node is expanded, and
	 *         <code>false</code> if collapsed
	 */
	public boolean getExpandedState(Object elementOrTreePath) {
		Assert.isNotNull(elementOrTreePath);
		Widget item = internalGetWidgetToSelect(elementOrTreePath);
		if (item instanceof Item) {
			return getExpanded((Item) item);
		}
		return false;
	}
	/**
	 * Returns the number of child items of the given SWT control.
	 *
	 * @param control
	 *            the control
	 * @return the number of children
	 */
	protected abstract int getItemCount(Control control);
	/**
	 * Returns the number of child items of the given SWT item.
	 *
	 * @param item
	 *            the item
	 * @return the number of children
	 */
	protected abstract int getItemCount(Item item);
	/**
	 * Returns the child items of the given SWT item.
	 *