anchor.diff:    final ui.TextDecoration _decoration;
     final ui.Color _decorationColor;
     final ui.TextDecorationStyle _decorationStyle;
  +  final double _decorationThickness;
     final ui.FontWeight _fontWeight;
     final ui.FontStyle _fontStyle;
     final ui.TextBaseline _textBaseline;
     final bool _isFontFamilyProvided;
     final String _fontFamily;
     final List<String> _fontFamilyFallback;
  +  final List<ui.FontFeature> _fontFeatures;
     final double _fontSize;
     final double _letterSpacing;
     final double _wordSpacing;
  
positive.code:         _decoration = decoration,
          _decorationColor = decorationColor,
          _decorationStyle = decorationStyle,
          _fontWeight = fontWeight,
          _fontStyle = fontStyle,
          _textBaseline = textBaseline,
          // TODO(b/128311960): when font fallback is supported, we should check
          //                    for it here.
          _isFontFamilyProvided = fontFamily != null,
          _fontFamily = fontFamily ?? '',
          // TODO(b/128311960): add support for font family fallback.
          _fontFamilyFallback = fontFamilyFallback,
          _fontSize = fontSize,
          _letterSpacing = letterSpacing,
          _wordSpacing = wordSpacing,
  
negative.code:           'decoration: ${_decoration ?? "unspecified"}, '
            'decorationColor: ${_decorationColor ?? "unspecified"}, '
            'decorationStyle: ${_decorationStyle ?? "unspecified"}, '
            'decorationThickness: ${_decorationThickness ?? "unspecified"}, '
            'fontWeight: ${_fontWeight ?? "unspecified"}, '
            'fontStyle: ${_fontStyle ?? "unspecified"}, '
            'textBaseline: ${_textBaseline ?? "unspecified"}, '
  