private long typedSum(Activity activity) {
        long sum = 0L;
        for (Tag tag : tags) {
            sum += fetchTime(activity, tag);
        }
        return sum;
    }
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