Update charted to 0.4.8 and roll

packages/async/lib/src/delegate/future.dart

 // Copyright (c) 2015, 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.
 
-library async.delegate.future;
+import 'dart:async';
 
-import 'dart:async';
+import '../typed/future.dart';
 
 /// A wrapper that forwards calls to a [Future].
 class DelegatingFuture<T> implements Future<T> {
   /// The wrapped [Future].
-  final Future _future;
+  final Future<T> _future;
 
   DelegatingFuture(this._future);
 
+  /// Creates a wrapper which throws if [future]'s value isn't an instance of
+  /// `T`.
+  ///
+  /// This soundly converts a [Future] to a `Future<T>`, regardless of its
+  /// original generic type, by asserting that its value is an instance of `T`
+  /// whenever it's provided. If it's not, the future throws a [CastError].
+  static Future<T> typed<T>(Future future) =>
+      future is Future<T> ? future : new TypeSafeFuture<T>(future);
+
   Stream<T> asStream() => _future.asStream();
 
-  Future catchError(Function onError, {bool test(error)}) =>
-    _future.catchError(onError, test: test);
+  Future<T> catchError(Function onError, {bool test(Object error)}) =>
+      _future.catchError(onError, test: test);
 
-  Future then(onValue(T value), {Function onError}) =>
-    _future.then(onValue, onError: onError);
+  Future<S> then<S>(FutureOr<S> onValue(T value), {Function onError}) =>
+      _future.then(onValue, onError: onError);
 
   Future<T> whenComplete(action()) => _future.whenComplete(action);
 
-  Future timeout(Duration timeLimit, {void onTimeout()}) =>
-    _future.timeout(timeLimit, onTimeout: onTimeout);
+  Future<T> timeout(Duration timeLimit, {onTimeout()}) =>
+      _future.timeout(timeLimit, onTimeout: onTimeout);
 }