Modernize the package's style.

lib/src/result/value.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';
+import 'error.dart';
+
+/// A result representing a returned value.
+class ValueResult<T> implements Result<T> {
+  final T value;
+
+  bool get isValue => true;
+  bool get isError => false;
+  ValueResult<T> get asValue => this;
+  ErrorResult get asError => null;
+
+  ValueResult(this.value);
+
+  void complete(Completer<T> completer) {
+    completer.complete(value);
+  }
+
+  void addTo(EventSink<T> sink) {
+    sink.add(value);
+  }
+
+  Future<T> get asFuture => new Future.value(value);
+}