dart:io | Add Link class, as sibling to File and Directory.

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;
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
   static const READ = const FileMode._internal(0);
   static const WRITE = const FileMode._internal(1);
   static const APPEND = const FileMode._internal(2);
   const FileMode._internal(int this._mode);
   final int _mode;
 }
 
 
 /**
  * [File] objects are references to files.
  *
+ * If [path] is a symbolic link, rather than a file, then
+ * the methods of [File] operate on the ultimate target of the
+ * link, except for File.delete and File.deleteSync, which operate on
+ * the link.
+ *
  * To operate on the underlying file data there are two options:
  *
  *  * Use streaming: read the contents of the file from the [Stream]
  *    this.[openRead]() and write to the file by writing to the [IOSink]
  *    this.[openWrite]().
  *  * Open the file for random access operations using [open].
  */
 abstract class File extends FileSystemEntity {
   /**
    * Create a File object.
@@ skipping 436 matching lines @@
         sb.write(" ($osError)");
       }
     } else if (osError != null) {
       sb.write(": osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }