Add support for file locking

sdk/lib/io/io_service.dart

Index: sdk/lib/io/io_service.dart
diff --git a/sdk/lib/io/io_service.dart b/sdk/lib/io/io_service.dart
index 4becb03a8590c121b4186daa5fecd95590230fc3..03db8adf131f3886734c48b5f8b7f4e0d8afa6ac 100644
--- a/sdk/lib/io/io_service.dart
+++ b/sdk/lib/io/io_service.dart
@@ -32,18 +32,19 @@ 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);