Make FileSystemEntity.watch return a broadcast stream.

runtime/bin/file_patch.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.
 
 patch class _File {
   /* patch */ static _exists(String path) native "File_Exists";
   /* patch */ static _create(String path) native "File_Create";
   /* patch */ static _createLink(String path, String target)
       native "File_CreateLink";
   /* patch */ static _linkTarget(String path) native "File_LinkTarget";
@@ skipping 43 matching lines @@
 
   StreamController _controller;
   StreamSubscription _subscription;
 
   _FileSystemWatcherImpl(this._path, this._events, this._recursive) {
     if (!isSupported) {
       throw new FileSystemException(
           "File system watching is not supported on this system",
           _path);
     }
-    _controller = new StreamController(onListen: _listen, onCancel: _cancel);
+    _controller = new StreamController.broadcast(onListen: _listen,
+                                                 onCancel: _cancel);
   }
 
   void _listen() {
     int socketId;
     try {
       socketId = _watchPath(_path, _events, identical(true, _recursive));
     } catch (e) {
       throw new FileSystemException(
           "Failed to watch path",
           _path,
@@ skipping 82 matching lines @@
 
   int _watchPath(String path, int events, bool recursive)
       native "FileSystemWatcher_WatchPath";
   void _unwatchPath() native "FileSystemWatcher_UnwatchPath";
   List _readEvents() native "FileSystemWatcher_ReadEvents";
 }
 
 Uint8List _makeUint8ListView(Uint8List source, int offsetInBytes, int length) {
   return new Uint8List.view(source.buffer, offsetInBytes, length);
 }