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
private Object element;
		private Item item;
		UpdateItemSafeRunnable(Item item, Object element) {
			this.item = item;
			this.element = element;
		}
		public void run() {
			doUpdateItem(item, element);
		}
	}
	/**
	 * Creates an abstract tree viewer. The viewer has no input, no content
	 * provider, a default label provider, no sorter, no filters, and has
	 * auto-expand turned off.
	 */
	protected AbstractTreeViewer() {
		
	}
	/**
	 * Adds the given child elements to this viewer as children of the given