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
if (event.item.getData() != null) {
			fireTreeExpanded(new TreeExpansionEvent(this, event.item.getData()));
		}
	}
	
	protected void hookControl(Control control) {
		super.hookControl(control);
		addTreeListener(control, new TreeListener() {
			public void treeExpanded(TreeEvent event) {
				handleTreeExpand(event);
			}
			public void treeCollapsed(TreeEvent event) {
				handleTreeCollapse(event);
			}
		});
	}
	/*
	 * (non-Javadoc) Method declared on StructuredViewer. Builds the initial
	 * tree and handles the automatic expand feature.
	 */
	protected void inputChanged(Object input, Object oldInput) {
		preservingSelection(new Runnable() {
			public void run() {
				Control tree = getControl();
				boolean useRedraw = true;
				
				
				if (useRedraw) {
					tree.setRedraw(false);
				}