Update charted to 0.4.8 and roll

packages/async/lib/src/single_subscription_transformer.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';
+
+/// A transformer that converts a broadcast stream into a single-subscription
+/// stream.
+///
+/// This buffers the broadcast stream's events, which means that it starts
+/// listening to a stream as soon as it's bound.
+///
+/// This also casts the source stream's events to type `T`. If the cast fails,
+/// the result stream will emit a [CastError]. This behavior is deprecated, and
+/// should not be relied upon.
+class SingleSubscriptionTransformer<S, T> implements StreamTransformer<S, T> {
+  const SingleSubscriptionTransformer();
+
+  Stream<T> bind(Stream<S> stream) {
+    var subscription;
+    var controller = new StreamController<T>(
+        sync: true, onCancel: () => subscription.cancel());
+    subscription = stream.listen((value) {
+      // TODO(nweiz): When we release a new major version, get rid of the second
+      // type parameter and avoid this conversion.
+      try {
+        controller.add(value as T);
+      } on CastError catch (error, stackTrace) {
+        controller.addError(error, stackTrace);
+      }
+    }, onError: controller.addError, onDone: controller.close);
+    return controller.stream;
+  }
+}