@Override
    protected SearchChains newChainsInstance(TreeConfigProducer<AnyConfigProducer> parent) {
        return new SearchChains(parent, "searchchains");
    }
Builds the search chains model from xml.

@author Tony Vaagenes
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/search/DomSearchChainsBuilder.java