@Override
    public com.google.web.bindery.event.shared.HandlerRegistration addDataSelectionHandler(
            final DataSelectionHandler<Selection<Long>> handler) {
        return addHandlerToSource(DataSelectionEvent.getType(), handler);
    }
@return The effective criteria taking into account the active filter and any
row selections.
stroom-core-client/src/main/java/stroom/data/client/presenter/AbstractMetaListPresenter.java