public int getInstanceCount(String zone) {
        if (zone == null) {
            return 0;
        }
        zone = zone.toLowerCase();
        List<? extends Server> currentList = upServerListZoneMap.get(zone);
        if (currentList == null) {
            return 0;
        }
        return currentList.size();
    }
Method that updates the internal stats of Response times maintained on a per Server
basis
@param server
@param msecs
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/LoadBalancerStats.java