Make StreamController take on{Pause,Subscription]StateChange as arguments.

sdk/lib/async/stream_impl.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;
 
 // States shared by single/multi stream implementations.
 
 /// Initial and default state where the stream can receive and send events.
 const int _STREAM_OPEN = 0;
@@ skipping 703 matching lines @@
       stream._sendDone();
       _isDone = true;
     }
   }
 }
 
 
 /**
  * The subscription class that the [StreamController] uses.
  *
- * The [StreamController.createSubscription] method should
+ * The [_StreamImpl.createSubscription] method should
  * create an object of this type, or another subclass of [_StreamListener].
- * A subclass of [StreamController] can specify which subclass
+ * A subclass of [_StreamImpl] can specify which subclass
  * of [_StreamSubscriptionImpl] it uses by overriding
- * [StreamController.createSubscription].
+ * [_StreamImpl.createSubscription].
  *
  * The subscription is in one of three states:
  * * Subscribed.
  * * Paused-and-subscribed.
  * * Unsubscribed.
- * Unsubscribing also unpauses.
+ * Unsubscribing also resumes any pauses started by the subscription.
  */
 class _StreamSubscriptionImpl<T> extends _StreamListener<T>
                                  implements StreamSubscription<T> {
   final bool _unsubscribeOnError;
   // TODO(ahe): Restore type when feature is implemented in dart2js
   // checked mode. http://dartbug.com/7733
   var /* _DataHandler<T> */ _onData;
   _ErrorHandler _onError;
   _DoneHandler _onDone;
   _StreamSubscriptionImpl(_StreamImpl source,
@@ skipping 414 matching lines @@
                                      onError: this._signalError,
                                      onDone: this._close);
     } else {
       // TODO(lrn): Check why this can happen.
       if (_subscription == null) return;
       _subscription.cancel();
       _subscription = null;
     }
   }
 }