private synchronized void updateTimeTrackingBeforeRun() {
    timeOfLastRun = timeOfThisRun;
    timeOfThisRun = EnvironmentEdgeManager.currentTime();
  }
Update our time tracking members. Called at the start of an execution of this chore's run()
method so that a correct decision can be made as to whether or not we missed the start time
hbase-common/src/main/java/org/apache/hadoop/hbase/ScheduledChore.java