Bug 127861 [DataBinding] Mark API provisional
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/viewers/UpdatableSetContentProvider.java
private IReadableSet readableSet = EmptyReadableSet.getInstance();
    private Viewer viewer;
    private IFilter filter = AcceptAllFilter.getInstance();
    private class KnownElementsSet extends AbstractUpdatableSet {
        protected Collection computeElements() {
            return readableSet.toCollection();
        }
         void doFireAdd(Collection added) {
            fireAdded(added);
        }
         void doFireRemove(Collection removed) {
            fireRemoved(removed);
        }