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
updateChildren(widget, parent, elementChildren, true);
	}
	/**
	 * Updates the tree items to correspond to the child elements of the given
	 * parent element. If null is passed for the children, this method obtains
	 * them (only if needed).
	 * 
	 * @param widget
	 *            the widget
	 * @param parent
	 *            the parent element
	 * @param elementChildren
	 *            the child elements, or null
	 * @param updateLabels
	 *            <code>true</code> to update labels for existing elements,
	 *            <code>false</code> to only update labels as needed, assuming
	 *            that labels for existing elements are unchanged.
	 * @since 2.1
	 */
	private void updateChildren(Widget widget, Object parent,
			Object[] elementChildren, boolean updateLabels) {
		
		if (widget instanceof Item) {
			Item ti = (Item) widget;
			if (!getExpanded(ti)) {
				
				
				boolean needDummy = isExpandable(ti, null, parent);
				boolean haveDummy = false;