private void activityRepr(StringBuilder buffer, int preLen,
                Map.Entry<Activity, Long> m) {
            if (buffer.length() != preLen) {
                buffer.append(", ");
            }
            buffer.append(m.getKey()).append(": ").append(m.getValue())
                    .append(" ms");
        }
A container for storing time stamps throughout the lifetime of an Execution instance.

<p>Check state both when entering and exiting, to allow for arbitrary
new queries anywhere inside a search chain.

@author Steinar Knutsen
container-search/src/main/java/com/yahoo/search/statistics/TimeTracker.java