Implement File.lastModified.

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._internal(0);
@@ skipping 74 matching lines @@
    * completes with the length in bytes.
    */
   Future<int> length();
 
   /**
    * Synchronously get the length of the file.
    */
   int lengthSync();
 
   /**
+   * Get the last-modified time of the file. Returns a
+   * [:Future<Date>:] that completes with a [Date] object for the
+   * modification date.
+   */
+  Future<Date> lastModified();
+
+  /**
+   * Get the last-modified time of the file. Throws an exception
+   * if the file does not exist.
+   */
+  Date lastModifiedSync();
+
+  /**
    * Open the file for random access operations. Returns a
    * [:Future<RandomAccessFile>:] that completes with the opened
    * random access file. RandomAccessFiles must be closed using the
    * [close] method.
    *
    * Files can be opened in three modes:
    *
    * FileMode.READ: open the file for reading.
    *
    * FileMode.WRITE: open the file for both reading and writing and
@@ skipping 263 matching lines @@
         sb.add(" ($osError)");
       }
     } else if (osError != null) {
       sb.add(": osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }