anchor.diff:     * Get a [Converter] for encoding to `ZLib` compressed data.
      */
     Converter<List<int>, List<int>> get encoder =>
  -      const ZLibEncoder(gzip: false, level: level);
  +      new ZLibEncoder(gzip: false, level: level);
   
     /**
      * Get a [Converter] for decoding `ZLib` compressed data.
  
positive.code:   void addSlice(List<int> data, int start, int end, bool isLast) {
      if (_closed) return;
      if (start < 0 || start > data.length) {
        throw ArgumentError("Invalid start position");
      }
      if (end < 0 || end > data.length || end < start) {
        throw ArgumentError("Invalid end position");
      }
      try {
        _empty = false;
  
negative.code: 
    void addSlice(List<int> chunk, int start, int end, bool isLast) {
      if (chunk is Uint8List) {
        var list = chunk as Uint8List;
        builder.add(new Uint8List.view(list.buffer, start, end - start));
      } else {
        builder.add(chunk.sublist(start, end));
      }
    }
  
  