void add(Coverage source) {
        answeredDocs += source.getDocs();
        answeredActiveDocs += source.getActive();
        answeredTargetActiveDocs += source.getTargetActive();
        answeredNodesParticipated += source.getNodes();
        answeredNodes++;
        degradedReason |= source.getDegradedReason();
    }
Aggregates coverage as responses are added.

@author baldersheim
container-search/src/main/java/com/yahoo/search/dispatch/CoverageAggregator.java