Make StreamController's unnamed constructor create a single-sub stream.

sdk/lib/isolate/isolate_stream.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.isolate;
 
 /**
  * The initial [IsolateStream] available by default for this isolate. This
  * [IsolateStream] is created automatically and it is commonly used to establish
  * the first communication between isolates (see [streamSpawnFunction] and
@@ skipping 34 matching lines @@
 
 /**
  * [IsolateStream]s, together with [IsolateSink]s, are the only means of
  * communication between isolates. Each IsolateStream has a corresponding
  * [IsolateSink]. Any message written into that sink will be delivered to
  * the stream and then dispatched to the stream's subscribers.
  */
 class IsolateStream extends Stream<dynamic> {
   bool _isClosed = false;
   final ReceivePort _port;
-  StreamController _controller = new StreamController();
+  StreamController _controller = new StreamController.multiSubscription();
 
   IsolateStream._fromOriginalReceivePort(this._port) {
     _port.receive((message, replyTo) {
       assert(replyTo == null);
       _add(message);
     });
   }
 
   IsolateStream._fromOriginalReceivePortOneShot(this._port) {
     _port.receive((message, replyTo) {
@@ skipping 140 matching lines @@
  * Creates and spawns an isolate whose code is available at [uri].  Like with
  * [streamSpawnFunction], the child isolate will have a default [IsolateStream],
  * and a this function returns an [IsolateSink] feeding into it.
  *
  * See comments at the top of this library for more details.
  */
 IsolateSink streamSpawnUri(String uri) {
   SendPort sendPort = spawnUri(uri);
   return new IsolateSink._fromPort(sendPort);
 }