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

@author gjoranv
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/docproc/DomDocprocChainsBuilder.java