Make new StreamController be async by default.

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;
 
 /** Throws the given error in the next cycle. */
 _throwDelayed(var error, [Object stackTrace]) {
   // We are going to reach the top-level here, but there might be a global
   // exception handler. This means that we shouldn't print the stack trace.
@@ skipping 676 matching lines @@
     }
     event.perform(dispatch);
   }
 
   void clear() {
     if (isScheduled) cancelSchedule();
     firstPendingEvent = lastPendingEvent = null;
   }
 }
 
-class _MultiplexerLinkedList {
-  _MultiplexerLinkedList _next;
-  _MultiplexerLinkedList _previous;
+class _BroadcastLinkedList {
+  _BroadcastLinkedList _next;
+  _BroadcastLinkedList _previous;
 
   void _unlink() {
     _previous._next = _next;
     _next._previous = _previous;
     _next = _previous = this;
   }
 
-  void _insertBefore(_MultiplexerLinkedList newNext) {
-    _MultiplexerLinkedList newPrevious = newNext._previous;
+  void _insertBefore(_BroadcastLinkedList newNext) {
+    _BroadcastLinkedList newPrevious = newNext._previous;
     newPrevious._next = this;
     newNext._previous = _previous;
     _previous._next = newNext;
     _previous = newPrevious;
   }
 }
 
 class _AsBroadcastStream<T> extends Stream<T> {
   final Stream<T> _source;
-  _BufferingMultiplexStreamController<T> _controller;
+  _AsBroadcastStreamController<T> _controller;
   StreamSubscription<T> _subscription;
 
   _AsBroadcastStream(this._source) {
-    _controller = new _BufferingMultiplexStreamController<T>(null, _onCancel);
+    _controller = new _AsBroadcastStreamController<T>(null, _onCancel);
   }
 
   bool get isBroadcast => true;
 
   StreamSubscription<T> listen(void onData(T data),
                                { void onError(Object error),
                                  void onDone(),
                                  bool cancelOnError}) {
     if (_controller == null) {
       throw new StateError("Source stream has been closed.");
@@ skipping 159 matching lines @@
       _FutureImpl<bool> hasNext = _futureOrPrefetch;
       _clear();
       hasNext._setValue(false);
       return;
     }
     _subscription.pause();
     _futureOrPrefetch = null;
     _state = _STATE_EXTRA_DONE;
   }
 }