Add typed wrapper functions to delegate classes.

lib/src/typed/stream_subscription.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';
+
+class TypeSafeStreamSubscription<T> implements StreamSubscription<T> {
+  final StreamSubscription _subscription;
+
+  bool get isPaused => _subscription.isPaused;
+
+  TypeSafeStreamSubscription(this._subscription);
+
+  void onData(void handleData(T data)) {
+    _subscription.onData((data) => handleData(data as T));
+  }
+
+  void onError(Function handleError) {
+    _subscription.onError(handleError);
+  }
+
+  void onDone(void handleDone()) {
+    _subscription.onDone(handleDone);
+  }
+
+  void pause([Future resumeFuture]) {
+    _subscription.pause(resumeFuture);
+  }
+
+  void resume() {
+    _subscription.resume();
+  }
+
+  Future cancel() => _subscription.cancel();
+  Future asFuture([futureValue]) => _subscription.asFuture(futureValue);
+}