@Override
    void add(MetricValue val) {
        GaugeMetric rhs = (GaugeMetric)val;
        last = rhs.last;
        if (rhs.max > max) {
            max = rhs.max;
        }
        if (rhs.min < min) {
            min = rhs.min;
        }
        sum += rhs.sum;
        count += rhs.count;
    }
A metric which contains a gauge value, i.e a value which represents the magnitude of something
measured at a point in time. This metric value contains some additional information about the distribution
of this gauge value in the time interval this metric is for.

@author Simon Thoresen Hult
container-core/src/main/java/com/yahoo/container/jdisc/state/GaugeMetric.java