Add support for file locking

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 20 matching lines @@
       native "File_ReadInto";
   /* patch */ static _writeByte(int id, int value) native "File_WriteByte";
   /* patch */ static _writeFrom(int id, List<int> buffer, int start, int end)
       native "File_WriteFrom";
   /* patch */ static _position(int id) native "File_Position";
   /* patch */ static _setPosition(int id, int position)
       native "File_SetPosition";
   /* patch */ static _truncate(int id, int length) native "File_Truncate";
   /* patch */ static _length(int id) native "File_Length";
   /* patch */ static _flush(int id) native "File_Flush";
+  /* patch */ static _lock(int id, int lock, int start, int end)
+      native "File_Lock";
 }
 
 
 class _WatcherPath {
   final int pathId;
   final String path;
   final int events;
   int count = 0;
   _WatcherPath(this.pathId, this.path, this.events);
 }
@@ skipping 308 matching lines @@
   void _pathWatchedEnd() {
     _subscription.cancel();
     _controller.close();
   }
 }
 
 
 Uint8List _makeUint8ListView(Uint8List source, int offsetInBytes, int length) {
   return new Uint8List.view(source.buffer, offsetInBytes, length);
 }