Roll Observatory packages and add a roll script

charted/lib/core/utils/disposer.dart

-//
-// Copyright 2014 Google Inc. All rights reserved.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-//
-
-part of charted.core.utils;
-
-class SubscriptionsDisposer {
-  List<StreamSubscription> _subscriptions = [];
-  Expando<StreamSubscription> _byObject = new Expando();
-
-  void add(StreamSubscription value, [Object handle]) {
-    if (handle != null) _byObject[handle] = value;
-    _subscriptions.add(value);
-  }
-
-  void addAll(Iterable<StreamSubscription> values, [Object handle]) {
-    for (var subscription in values) {
-      add(subscription, handle);
-    }
-  }
-
-  void unsubscribe(Object handle) {
-    StreamSubscription s = _byObject[handle];
-    if (s != null) {
-      _subscriptions.remove(s);
-      s.cancel();
-    }
-  }
-
-  void dispose() {
-    _subscriptions.forEach((StreamSubscription val) {
-      if (val != null) val.cancel();
-    });
-    _subscriptions = [];
-  }
-}