Add asynchronous versions of the methods on Directory.

runtime/bin/directory.dart

Index: runtime/bin/directory.dart
diff --git a/runtime/bin/directory.dart b/runtime/bin/directory.dart
index acdcd09444312e0f95e231102ee08d697700ee9c..5bde4ac1c09929cebfd889eb35bf60f8d8fc823c 100644
--- a/runtime/bin/directory.dart
+++ b/runtime/bin/directory.dart
@@ -11,13 +11,27 @@ interface Directory factory _Directory {
   Directory(String path);
 
   /**
-   * Returns whether a directory with this name already exists.
+   * Check whether a directory with this name already exists. If the
+   * operation completes successfully the [existsHandler] is called with
+   * the result. Otherwise the [errorHandler] is called.
+   */
+  void exists();
+
+  /**
+   * Synchronously check whether a directory with this name already exists.
    */
   bool existsSync();
 
   /**
    * Creates the directory with this name if it does not exist.
-   * Throw an exception if the directory already exists.
+   * If the directory is successfully created the [createHandler] is
+   * called. Otherwise the [errorHandler] is called.
+   */
+  void create();
+
+  /**
+   * Synchronously creates the directory with this name if it does not exist.
+   * Throws an exception if the directory already exists.
    */
   void createSync();
 
@@ -45,6 +59,13 @@ interface Directory factory _Directory {
   void createTempSync();
 
   /**
+   * Deletes the directory with this name. If the operation completes
+   * successfully the [deleteHandler] is called. Otherwise the
+   * [errorHandler] is called.
+   */
+  void delete();
+
+  /**
    * Deletes the directory with this name. Throws an exception
    * if the directory is not empty or if deletion failed.
    */
@@ -82,12 +103,29 @@ interface Directory factory _Directory {
   void set doneHandler(void doneHandler(bool completed));
 
   /**
+   * Set the handler that is called when checking if a directory with this
+   * name exists.
+   */
+  void set existsHandler(void existsHandler(bool exists));
+
+  /**
+   * Set the handler that is called when a directory is successfully created.
+   */
+  void set createHandler(void createHandler());
+
+  /**
    * Set the handler that is called when a temporary directory is
    * successfully created.
    */
   void set createTempHandler(void doneHandler(bool completed));
 
   /**
+   * Set the handler that is called when a directory is successfully
+   * deleted.
+   */
+  void set deleteHandler(void deleteHandler());
+
+  /**
    * Sets the handler that is called if there is an error while listing
    * or creating directories.
    */