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
/**
	 * Adds a listener for expand and collapse events in this viewer. Has no
	 * effect if an identical listener is already registered.
	 * 
	 * @param listener
	 *            a tree viewer listener
	 */
	public void addTreeListener(ITreeViewerListener listener) {
		treeListeners.add(listener);
	}
	/**
	 * Adds the given SWT tree listener to the given SWT control.
	 * 
	 * @param control
	 *            the SWT control
	 * @param listener
	 *            the SWT tree listener
	 */
	protected abstract void addTreeListener(Control control,
			TreeListener listener);
	/*
	 * (non-Javadoc)
	 * 
	 * @see StructuredViewer#associate(Object, Item)
	 */
	protected void associate(Object element, Item item) {
		Object data = item.getData();
		if (data != null && data != element && equals(data, element)) {