Bug 93400 LTK UI should provide official API for structural content in the preview page
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/internal/ui/refactoring/PreviewWizardPage.java
fActiveAction= fShowAllAction;
			fFilterActions= new FilterAction[groupCategories.size()];
			int i= 0;
			for (Iterator iter= groupCategories.iterator(); iter.hasNext();) {
				fFilterActions[i++]= new FilterAction(this, (GroupCategory)iter.next());
			}
			setEnabled(groupCategories.size() > 0);
		}
		public void dispose() {
			if (fMenu != null) {
				fMenu.dispose();
				fMenu= null;				
			}
		}
		public Menu getMenu(Control parent) {
			dispose();
			fMenu= new Menu(parent);
			new ActionContributionItem(fShowAllAction).fill(fMenu, -1);
			new MenuItem(fMenu, SWT.SEPARATOR);
			for (int i= 0; i < fFilterActions.length; i++) {
				new ActionContributionItem(fFilterActions[i]).fill(fMenu, -1);
			}
			return fMenu;
		}
		public Menu getMenu(Menu parent) {
			return null;
		}
		public void executed(Action action) {
			if (fActiveAction == action)
				return;