anchor.diff:      return new SnackBar(
         key: key ?? fallbackKey,
         content: content,
  +      backgroundColor: backgroundColor,
         action: action,
         duration: duration,
         animation: newAnimation
  
positive.code:   SnackBar({
      Key key,
      this.content,
      this.action,
      this.duration: _kSnackBarDisplayDuration,
      this.animation
  
negative.code:   ///
    /// Typically a [Text] widget.
    final Widget content;
  
    /// The Snackbar's background color. By default the color is dark grey.
    final Color backgroundColor;
  
    /// (optional) An action that the user can take based on the snack bar.
    ///
  