public void addEntry(String text, long timestamp) {
        mData.add(new Pair<String, Long>(text, timestamp));
    }
Adds a new entry to the log.
@param text the text to be stored in the log
@param timestamp the current time in milliseconds since January 1, 1970 00:00:00.0 UTC.
unit/BasicUnitAndroidTest/app/src/main/java/com/example/android/testing/unittesting/basicunitandroidtest/LogHistory.java