Add a bunch of delegates for dart:async types.

lib/src/delegating_stream_subscription.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.delegating_stream_subscription;
-
-import 'dart:async';
-
-/// Simple delegating wrapper around a [StreamSubscription].
-///
-/// Subclasses can override individual methods.
-class DelegatingStreamSubscription<T> implements StreamSubscription<T> {
-  final StreamSubscription _source;
-
-  /// Create delegating subscription forwarding calls to [sourceSubscription].
-  DelegatingStreamSubscription(StreamSubscription sourceSubscription)
-      : _source = sourceSubscription;
-
-  void onData(void handleData(T data)) {
-    _source.onData(handleData);
-  }
-
-  void onError(Function handleError) {
-    _source.onError(handleError);
-  }
-
-  void onDone(void handleDone()) {
-    _source.onDone(handleDone);
-  }
-
-  void pause([Future resumeFuture]) {
-    _source.pause(resumeFuture);
-  }
-
-  void resume() {
-    _source.resume();
-  }
-
-  Future cancel() => _source.cancel();
-
-  Future asFuture([futureValue]) => _source.asFuture(futureValue);
-
-  bool get isPaused => _source.isPaused;
-}