Fix wrong return type on fullPath in File API.

runtime/bin/file.dart

 // Copyright (c) 2011, 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);
@@ skipping 88 matching lines @@
    *
    * FileMode.APPEND: same as FileMode.WRITE except that the file is
    * not truncated.
    *
    * By default mode is FileMode.READ.
    */
   RandomAccessFile openSync([FileMode mode]);
 
   /**
    * Get the canonical full path corresponding to the file name. The
-   * [fullPathHandler] is called when the fullPath operation
-   * completes.
+   * [fullPathHandler] is called with the result when the fullPath
+   * operation completes.
    */
-  String fullPath();
+  void fullPath();
 
   /**
    * Synchronously get the canonical full path corresponding to the file name.
    */
   String fullPathSync();
 
   /**
    * Create a new independent input stream for the file. The file
    * input stream must be closed when no longer used to free up
    * system resources.
@@ skipping 170 matching lines @@
   void set flushHandler(void handler());
   void set errorHandler(void handler(String error));
 }
 
 
 class FileIOException implements Exception {
   const FileIOException([String this.message = ""]);
   String toString() => "FileIOException: $message";
   final String message;
 }