Add FileSystemEntity.absolutePath and .isAbsolute properties.

sdk/lib/io/file_impl.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;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 249 matching lines @@
   }
 
   external static _exists(String path);
 
   bool existsSync() {
     var result = _exists(path);
     throwIfError(result, "Cannot check existence of file", path);
     return result;
   }
 
+  File get absolute => new File(_absolutePath);
+
   Future<FileStat> stat() => FileStat.stat(path);
 
   FileStat statSync() => FileStat.statSync(path);
 
   Future<File> create() {
     _ensureFileService();
     List request = new List(2);
     request[0] = _CREATE_REQUEST;
     request[1] = path;
     return _fileService.call(request).then((response) {
@@ skipping 717 matching lines @@
   void _checkNotClosed() {
     if (closed) {
       throw new FileException("File closed", path);
     }
   }
 
   Future _closedException() {
     return new Future.error(new FileException("File closed", path));
   }
 }