public void addCallData(Collection<TimeHistogram> timeHistogramList) {
        for (TimeHistogram timeHistogram : timeHistogramList) {
            TimeHistogram histogram = getTimeHistogram(timeHistogram.getTimeStamp());
            histogram.add(timeHistogram);
        }
    }
representation of out/in relationship
@author emeroad
web/src/main/java/com/navercorp/pinpoint/web/applicationmap/rawdata/LinkCallData.java