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/ChangeElementTreeViewer.java
while(parent != null) {
					int active= parent.getActive();
					parent.setEnabledShallow(active == ChangeElement.PARTLY_ACTIVE || active == ChangeElement.ACTIVE);
					boolean grayed= (active == ChangeElement.PARTLY_ACTIVE);
					setChecked(parent, checked ? true : grayed);
					setGrayed(parent, grayed);
					parent= parent.getParent();
				}
			}
		});
	}
	
	public void setGroupCategory(List groupCategories) {
		((GroupCategoryFilter)(getFilters()[0])).setGroupCategory(groupCategories);
		try {
			fDeferredTreeItemUpdates= new ArrayList();
			refresh();
			processDeferredTreeItemUpdates();
		} finally  {
			fDeferredTreeItemUpdates= null;
		}
	}
	
	protected void inputChanged(Object input, Object oldInput) {
		try {
			fDeferredTreeItemUpdates= new ArrayList();
			super.inputChanged(input, oldInput);
			processDeferredTreeItemUpdates();
		} finally {
			fDeferredTreeItemUpdates= null;