Bug 161086 [Viewers] performance problem in AbstractTreeViewer.internalExpandToLevel
If you expand to ALL_LEVELS, internalExpandToLevel will call createChildren even if the element has no children, i.e. it does not check if the element is expandable. Found this while experimenting with the Quick Access feature (enter "con", then delete all three characters one at a time).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* 
	 * @param item
	 *            the widget
	 */
	private void disassociateChildren(Item item) {
		Item[] items = getChildren(item);
		for (int i = 0; i < items.length; i++) {
			if (items[i].getData() != null) {
				disassociate(items[i]);
			}
		}
	}
	
	protected Widget doFindInputItem(Object element) {
		
		Object root = getRoot();
		if (root == null) {
			return null;
		}
		if (equals(root, element)) {
			return getControl();
		}
		return null;
	}
	
	protected Widget doFindItem(Object element) {
		
		Object root = getRoot();
		if (root == null) {
			return null;