Remove Signal class and use Future/.whenComplete instead.

sdk/lib/async/stream_controller.dart

 // Copyright (c) 2012, 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.
 
 // part of dart.async;
 
 // -------------------------------------------------------------------
 // Default implementation of a stream with a controller for adding
 // events to the stream.
 // -------------------------------------------------------------------
@@ skipping 62 matching lines @@
 
   /** Whether one or more active subscribers have requested a pause. */
   bool get isPaused => _stream._isPaused;
 
   /** Whether there are currently any subscribers on this [Stream]. */
   bool get hasSubscribers => _stream._hasSubscribers;
 
   /**
    * Send or queue a data event.
    */
-  Signal add(T value) => _stream._add(value);
+  void add(T value) => _stream._add(value);
 
   /**
    * Send or enqueue an error event.
    *
    * If a subscription has requested to be unsubscribed on errors,
    * it will be unsubscribed after receiving this event.
    */
   void signalError(AsyncError error) { _stream._signalError(error); }
 
   /**
@@ skipping 53 matching lines @@
   _SingleControllerStream(this._subscriptionHandler, this._pauseHandler);
 
   void _onSubscriptionStateChange() {
     _subscriptionHandler();
   }
 
   void _onPauseStateChange() {
     _pauseHandler();
   }
 }