Implement File.directory() and File.directorySync() to get

runtime/bin/file.dart

Index: runtime/bin/file.dart
diff --git a/runtime/bin/file.dart b/runtime/bin/file.dart
index cfc5b77d3e67930d4cb9c518602d4e834d597d59..48687f6a91a0874c20ec03ee6248b4c13ba594a0 100644
--- a/runtime/bin/file.dart
+++ b/runtime/bin/file.dart
@@ -68,6 +68,20 @@ interface File default _File {
   void deleteSync();
 
   /**
+   * Get a Directory object for the directory containing this file. If
+   * the file does not exist the [errorHandler] is called. When the
+   * operation completes the [directoryHandler] is called with the
+   * result.
+   */
+  void directory();
+
+  /**
+   * Synchronously get a Directory object for the directory containing
+   * this file.
+   */
+  Directory directorySync();
+
+  /**
    * Open the file for random access operations. When the file is
    * opened the [openHandler] is called with the resulting
    * RandomAccessFile. RandomAccessFiles must be closed using the
@@ -185,6 +199,12 @@ interface File default _File {
   void set deleteHandler(void handler());
 
   /**
+   * Sets the handler that gets called when a [directory] operation
+   * completes.
+   */
+  void set directoryHandler(void handler(Directory directory));
+
+  /**
    * Sets the handler that gets called when an [open] operation
    * completes.
    */