Return the first time of the trip. TODO: For trips defined by frequency
    return the first time of the first trip.

def GetStartTime(self, problems=problems_module.default_problem_reporter):
    """Return the first time of the trip. TODO: For trips defined by frequency
    return the first time of the first trip."""
    cursor = self._schedule._connection.cursor()
    cursor.execute(
        'SELECT arrival_secs,departure_secs FROM stop_times WHERE '
        'trip_id=? ORDER BY stop_sequence LIMIT 1', (self.trip_id,))
    (arrival_secs, departure_secs) = cursor.fetchone()
    if arrival_secs != None:
      return arrival_secs
    elif departure_secs != None:
      return departure_secs
    else:
      problems.InvalidValue('departure_time', '',
                            'The first stop_time in trip %s is missing '
                            'times.' % self.trip_id)