Roll Observatory packages and add a roll script

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

Index: packages/async/lib/src/delegate/stream_consumer.dart
diff --git a/packages/async/lib/src/delegate/stream_consumer.dart b/packages/async/lib/src/delegate/stream_consumer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8162db6d8ec7886befc3902e664de3d2170453d4
--- /dev/null
+++ b/packages/async/lib/src/delegate/stream_consumer.dart
@@ -0,0 +1,23 @@
+// 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.stream_consumer;
+
+import 'dart:async';
+
+/// Simple delegating wrapper around a [StreamConsumer].
+///
+/// Subclasses can override individual methods, or use this to expose only the
+/// [StreamConsumer] methods of a subclass.
+class DelegatingStreamConsumer<T> implements StreamConsumer<T> {
+  final StreamConsumer _consumer;
+
+  /// Create a delegating consumer forwarding calls to [consumer].
+  DelegatingStreamConsumer(StreamConsumer consumer)
+      : _consumer = consumer;
+
+  Future addStream(Stream<T> stream) => _consumer.addStream(stream);
+
+  Future close() => _consumer.close();
+}