anchor.diff:  
   void main() {
     DateTime noFractionalSeconds = DateTime.utc(0, 1, 1, 0, 0, 0);
  +  Map<String, Skip> skipWeb = {
  +    'js': Skip(
  +        'Web does not support microseconds (see https://github.com/dart-lang/sdk/issues/44876)')
  +  };
     // Testing `decode`.
     test('Parse only year', () {
       var time = FixedDateTimeFormatter('YYYY').decode('1996');
  
positive.code:   test('Parse SSSSSS a microsecond', () {
      var time = FixedDateTimeFormatter('SSSSSS').decode('000001');
      expect(time, noFractionalSeconds.add(Duration(microseconds: 1)));
    });
    test('Parse SSSSSS a millisecond', () {
      var time = FixedDateTimeFormatter('SSSSSS').decode('001000');
      expect(time, noFractionalSeconds.add(Duration(milliseconds: 1)));
  
negative.code:     ));
      var str = FixedDateTimeFormatter('ssSSSSSS').encode(dateTime);
      expect(str, '01000001');
    }, onPlatform: skipWeb);
    test('Parse ssSSSSSSS a second and a microsecond', () {
      var dateTime = noFractionalSeconds.add(Duration(
        seconds: 1,
  