@Override
    public Trace clone() {
        try {
            return (Trace)super.clone();
        }
        catch (CloneNotSupportedException e) {
            throw new RuntimeException(e);
        }
    }
Traces how properties was resolved and from where. Done after the fact to avoid special handling
of tracelevel, which is the property deciding whether this needs to be done
container-search/src/main/java/com/yahoo/search/query/Trace.java