anchor.diff:  class _FileStreamConsumer extends StreamConsumer<List<int>> {
     File _file;
     Future<RandomAccessFile> _openFuture;
  -  StreamSubscription _subscription;
   
     _FileStreamConsumer(File this._file, FileMode mode) {
       _openFuture = _file.open(mode: mode);
     }
   
     Future<File> addStream(Stream<List<int>> stream) {
  -    Completer<File> completer = new Completer<File>();
  +    Completer<File> completer = new Completer<File>.sync();
       _openFuture
         .then((openedFile) {
  +        var _subscription;
           void error(e, [StackTrace stackTrace]) {
             _subscription.cancel();
             openedFile.close();
  
positive.code: 
    void _checkAvailable() {
      if (_asyncDispatched) {
        throw new FileSystemException("An async operation is currently pending", path);
      }
      if (closed) {
        throw new FileSystemException("File closed", path);
  
negative.code:   Future<File> writeAsBytes(List<int> bytes,
                              {FileMode mode: FileMode.WRITE,
                               bool flush: false}) {
      return open(mode: mode).then((file) {
        return file.writeFrom(bytes, 0, bytes.length)
            .then((_) {
              if (flush) return file.flush().then((_) => this);
              return this;
            })
            .whenComplete(file.close);
      });
    }
  
    void writeAsBytesSync(List<int> bytes,
  