Modernize the package's style.

lib/src/result/release_sink.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import '../result.dart';
+
+/// Use [Result.captureSinkTransformer].
+@Deprecated("Will be removed in async 2.0.0.")
+class ReleaseSink<T> implements EventSink<Result<T>> {
+  final EventSink _sink;
+
+  ReleaseSink(EventSink<T> sink) : _sink = sink;
+
+  void add(Result<T> result) {
+    if (result.isValue) {
+      _sink.add(result.asValue.value);
+    } else {
+      var error = result.asError;
+      _sink.addError(error.error, error.stackTrace);
+    }
+  }
+
+  void addError(Object error, [StackTrace stackTrace]) {
+    // Errors may be added by intermediate processing, even if it is never
+    // added by CaptureSink.
+    _sink.addError(error, stackTrace);
+  }
+
+  void close() {
+    _sink.close();
+  }
+}