anchor.diff:     * returns the difference as a new Duration object.
      */
     Duration operator -(Duration other) {
  -    return new Duration(microseconds: _duration - other._duration);
  +    return new Duration._microseconds(_duration - other._duration);
     }
   
     /**
  
positive.code:     // By doing the check here instead of relying on "~/" below we get the
      // exception even with dart2js.
      if (quotient == 0) throw new IntegerDivisionByZeroException();
      return new Duration(microseconds: _duration ~/ quotient);
    }
  
    /**
  
negative.code:     }
  
      if (inMicroseconds < 0) {
        return "-${-this}";
      }
      String twoDigitMinutes = twoDigits(inMinutes.remainder(MINUTES_PER_HOUR));
      String twoDigitSeconds = twoDigits(inSeconds.remainder(SECONDS_PER_MINUTE));
  