Make an enumeration added for 1.9 a real enum

sdk/lib/io/file.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;
 
 /**
  * The modes in which a File can be opened.
  */
 class FileMode {
@@ skipping 16 matching lines @@
 /// The mode for opening a file for reading and writing. The file is
 /// overwritten if it already exists. The file is created if it does not
 /// already exist.
 const WRITE = FileMode.WRITE;
 /// The mode for opening a file for reading and writing to the
 /// end of it. The file is created if it does not already exist.
 const APPEND = FileMode.APPEND;
 
 
 /// Type of lock when requesting a lock on a file.
-class FileLock {
-  final int _lock;
-
+enum FileLock {
   /// Shared file lock.
-  static const SHARED = const FileLock._internal(0);
-
+  SHARED,
   /// Exclusive file lock.
-  static const EXCLUSIVE = const FileLock._internal(1);
-
-  const FileLock._internal(this._lock);
+  EXCLUSIVE
 }
 
 /**
  * A reference to a file on the file system.
  *
  * A File instance is an object that holds a [path] on which operations can
  * be performed.
  * You can get the parent directory of the file using the getter [parent],
  * a property inherited from [FileSystemEntity].
  *
@@ skipping 809 matching lines @@
       sb.write(": $osError");
       if (path != null) {
         sb.write(", path = '$path'");
       }
     } else if (path != null) {
       sb.write(": $path");
     }
     return sb.toString();
   }
 }