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
IContentProvider cp = getContentProvider();
		if (cp instanceof ITreePathContentProvider) {
			ITreePathContentProvider tpcp = (ITreePathContentProvider) cp;
			TreePath[] paths = tpcp.getParents(elementOrTreePath);
			if (paths.length > 0) {
				if (paths[0].getSegmentCount() == 0) {
					return getInput();
				}
				return paths[0].getLastSegment();
			}
		}
		if (cp instanceof ITreeContentProvider) {
			ITreeContentProvider tcp = (ITreeContentProvider) cp;
			return tcp.getParent(elementOrTreePath);
		}
		return null;
	}
	/**
	 * Returns the widget to be selected for the given element or tree path.
	 * 
	 * @param elementOrTreePath
	 *            the element or tree path to select
	 * @return the widget to be selected, or <code>null</code> if not found
	 * 
	 * @since 3.1
	 */
	protected Widget internalGetWidgetToSelect(Object elementOrTreePath) {
		if (elementOrTreePath instanceof TreePath) {
			TreePath treePath = (TreePath) elementOrTreePath;
			if (treePath.getSegmentCount() == 0) {