Prevent creation of additional FileMode and Encoding objects

runtime/bin/file.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.
 
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
-  static final READ = const FileMode(0);
-  static final WRITE = const FileMode(1);
-  static final APPEND = const FileMode(2);
-  const FileMode(int this._mode);
+  static final READ = const FileMode._internal(0);
+  static final WRITE = const FileMode._internal(1);
+  static final APPEND = const FileMode._internal(2);
+  const FileMode._internal(int this._mode);
   final int _mode;
 }
 
 
 /**
  * [File] objects are references to files.
  *
  * To operate on the underlying file data you need to either get
  * streams using [openInputStream] and [openOutputStream] or open the
  * file for random access operations using [open].
@@ skipping 339 matching lines @@
    */
   void set onError(void handler(String error));
 }
 
 
 class FileIOException implements Exception {
   const FileIOException([String this.message = ""]);
   String toString() => "FileIOException: $message";
   final String message;
 }