Add FileSystemEntity.absolutePath and .isAbsolute properties.

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 {
@@ skipping 81 matching lines @@
   Future<int> length();
 
   /**
    * Synchronously get the length of the file.
    *
    * Throws a [FileException] if the operation fails.
    */
   int lengthSync();
 
   /**
+   * Returns a [File] instance whose path is the absolute path to [this].
+   *
+   * The absolute path is computed by prefixing
+   * a relative path with the current working directory, and returning
+   * an absolute path unchanged.
+   */
+  File get absolute;
+
+  /**
    * Get the last-modified time of the file. Returns a
    * [:Future<DateTime>:] that completes with a [DateTime] object for the
    * modification date.
    */
   Future<DateTime> lastModified();
 
   /**
    * Get the last-modified time of the file. Throws an exception
    * if the file does not exist.
    *
@@ skipping 413 matching lines @@
       }
     } else if (osError != null) {
       sb.write(": osError");
       if (path != null) {
         sb.write(", path = $path");
       }
     }
     return sb.toString();
   }
 }