Media Galleries: chrome.mediaGalleries.addUserSelectedFolder() requires a user gesture.

chrome/common/extensions/api/media_galleries.idl

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Use the <code>chrome.mediaGalleries</code> API to access media files (images,
 // video, audio) from the user's local disks (with the user's consent).
 namespace mediaGalleries {
 
   [inline_doc] enum GetMediaFileSystemsInteractivity {
     // Do not act interactively.
@@ skipping 86 matching lines @@
 
   interface Functions {
     // Get the media galleries configured in this user agent. If none are
     // configured or available, the callback will receive an empty array.
     static void getMediaFileSystems(optional MediaFileSystemsDetails details,
                                     MediaFileSystemsCallback callback);
 
     // Present a directory picker to the user and add the selected directory
     // as a gallery. If the user cancels the picker, selectedFileSystemName
     // will be empty.
+    // A user gesture is required for the dialog to display. Without a user
+    // gesture, the callback will run as though the user canceled.
     static void addUserSelectedFolder(AddUserFolderCallback callback);
 
     // Get metadata about a specific media file system.
     [nocompile] static MediaFileSystemMetadata getMediaFileSystemMetadata(
         [instanceOf=DOMFileSystem] object mediaFileSystem);
 
     // Get metadata for all available media galleries.
     static void getAllMediaFileSystemMetadata(
         MediaFileSystemsMetadataCallback callback);
                 
     // Gets the media-specific metadata for a media file. This should work
     // for files in media galleries as well as other DOM filesystems.
     static void getMetadata([instanceOf=Blob] object mediaFile,
                             optional MediaMetadataOptions options,
                             MediaMetadataCallback callback);
   };
 
 };