Update charted to 0.4.8 and roll

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

Index: packages/async/lib/src/delegate/stream_subscription.dart
diff --git a/packages/async/lib/src/delegate/stream_subscription.dart b/packages/async/lib/src/delegate/stream_subscription.dart
index ff9b66584b119a2373792e19450360d3fc962f4d..e7575d8215cb0dcf6a582321f51e99447aec23d0 100644
--- a/packages/async/lib/src/delegate/stream_subscription.dart
+++ b/packages/async/lib/src/delegate/stream_subscription.dart
@@ -2,10 +2,10 @@
 // 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.stream_subscription;
-
 import 'dart:async';
 
+import '../typed/stream_subscription.dart';
+
 /// Simple delegating wrapper around a [StreamSubscription].
 ///
 /// Subclasses can override individual methods.
@@ -13,9 +13,21 @@ class DelegatingStreamSubscription<T> implements StreamSubscription<T> {
   final StreamSubscription _source;
 
   /// Create delegating subscription forwarding calls to [sourceSubscription].
-  DelegatingStreamSubscription(StreamSubscription sourceSubscription)
+  DelegatingStreamSubscription(StreamSubscription<T> sourceSubscription)
       : _source = sourceSubscription;
 
+  /// Creates a wrapper which throws if [subscription]'s events aren't instances
+  /// of `T`.
+  ///
+  /// This soundly converts a [StreamSubscription] to a `StreamSubscription<T>`,
+  /// regardless of its original generic type, by asserting that its events are
+  /// instances of `T` whenever they're provided. If they're not, the
+  /// subscription throws a [CastError].
+  static StreamSubscription<T> typed<T>(StreamSubscription subscription) =>
+      subscription is StreamSubscription<T>
+          ? subscription
+          : new TypeSafeStreamSubscription<T>(subscription);
+
   void onData(void handleData(T data)) {
     _source.onData(handleData);
   }
@@ -38,7 +50,7 @@ class DelegatingStreamSubscription<T> implements StreamSubscription<T> {
 
   Future cancel() => _source.cancel();
 
-  Future asFuture([futureValue]) => _source.asFuture(futureValue);
+  Future<E> asFuture<E>([E futureValue]) => _source.asFuture(futureValue);
 
   bool get isPaused => _source.isPaused;
 }