toDuration method

Implementation

Duration toDuration() {
  num microseconds = 0;
  microseconds += year * DatePart.year.microseconds;
  microseconds += month * DatePart.mounth.microseconds;
  microseconds += day * DatePart.day.microseconds;
  microseconds += hour * DatePart.hour.microseconds;
  microseconds += minute * DatePart.minute.microseconds;
  microseconds += second * DatePart.second.microseconds;
  microseconds += millisecond * DatePart.millisecond.microseconds;
  microseconds += microsecond;
  return Duration(microseconds: microseconds.round());
}