private void addOuterComponents(CHAINS chains, ComponentsBuilder<COMPONENT> outerComponentsBuilder) {
        assert (outerComponentsBuilder.getOuterComponentReferences().isEmpty());

        for (ChainedComponent<?> outerComponent : outerComponentsBuilder.getComponentDefinitions()) {
            chains.add(outerComponent);
        }
    }
NOTE: This class _must_ be abstract, due to calling subclass method in ctor.
@author Tony Vaagenes
@author gjoranv
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/DomChainsBuilder.java