Add support for file locking

sdk/lib/io/io_service.dart

 // Copyright (c) 2013, 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.io;
 
 // This list must be kept in sync with the list in runtime/bin/io_service.h
 const int _FILE_EXISTS = 0;
 const int _FILE_CREATE = 1;
 const int _FILE_DELETE = 2;
@@ skipping 14 matching lines @@
 const int _FILE_READ = 17;
 const int _FILE_READ_INTO = 18;
 const int _FILE_WRITE_FROM = 19;
 const int _FILE_CREATE_LINK = 20;
 const int _FILE_DELETE_LINK = 21;
 const int _FILE_RENAME_LINK = 22;
 const int _FILE_LINK_TARGET = 23;
 const int _FILE_TYPE = 24;
 const int _FILE_IDENTICAL = 25;
 const int _FILE_STAT = 26;
-const int _SOCKET_LOOKUP = 27;
-const int _SOCKET_LIST_INTERFACES = 28;
-const int _SOCKET_REVERSE_LOOKUP = 29;
-const int _DIRECTORY_CREATE = 30;
-const int _DIRECTORY_DELETE = 31;
-const int _DIRECTORY_EXISTS = 32;
-const int _DIRECTORY_CREATE_TEMP = 33;
-const int _DIRECTORY_LIST_START = 34;
-const int _DIRECTORY_LIST_NEXT = 35;
-const int _DIRECTORY_LIST_STOP = 36;
-const int _DIRECTORY_RENAME = 37;
-const int _SSL_PROCESS_FILTER = 38;
+const int _FILE_LOCK = 27;
+const int _SOCKET_LOOKUP = 28;
+const int _SOCKET_LIST_INTERFACES = 29;
+const int _SOCKET_REVERSE_LOOKUP = 30;
+const int _DIRECTORY_CREATE = 31;
+const int _DIRECTORY_DELETE = 32;
+const int _DIRECTORY_EXISTS = 33;
+const int _DIRECTORY_CREATE_TEMP = 34;
+const int _DIRECTORY_LIST_START = 35;
+const int _DIRECTORY_LIST_NEXT = 36;
+const int _DIRECTORY_LIST_STOP = 37;
+const int _DIRECTORY_RENAME = 38;
+const int _SSL_PROCESS_FILTER = 39;
 
 class _IOService {
   external static Future dispatch(int request, List data);
 }