@Override
    public Result search(Query query, Execution execution) {
        Result result = execution.search(query);
        Result blended = blendResults(result, query, query.getOffset(), query.getHits(), execution);
        blended.trace("Blended result");
        return blended;
    }
Flattens a result consisting of multiple hit groups containing hits
into a single flat list of hits.

@author Bob Travis
@author Steinar Knutsen
@author Arne Fossaa
container-search/src/main/java/com/yahoo/prelude/searcher/BlendingSearcher.java