anchor.diff:    SnackBar({
       Key key,
       this.content,
  +    this.backgroundColor,
       this.action,
       this.duration: _kSnackBarDisplayDuration,
       this.animation
  
positive.code:     return new SnackBar(
        key: key ?? fallbackKey,
        content: content,
        action: action,
        duration: duration,
        animation: newAnimation
  
negative.code:             },
              child: new Material(
                elevation: 6,
                color: backgroundColor ?? _kSnackBackground,
                child: new Theme(
                  data: darkTheme,
                  child: new FadeTransition(
  