My original thought is that this would change to return something like Future<List<MediaFileSystem>> where MediaFileSystem has a reference to the js.Proxy and two  getters, root and readOnly (https://developer.mozilla.org/en-US/docs/Web/API/FileSystem). Then root getter should return an instance of ChromeFileEntry (as defined in file_system.dart).

However, even better would be if this was change to return something that implemented dart:html's FileSystem interface (http://api.dartlang.org/docs/releases/latest/dart_html/FileSystem.html) and related classes (as maybe should file_system.dart itself, although I question that since I think it overlaps http://api.dartlang.org/docs/releases/latest/dart_chrome/API_file_system.html).

Both of these are large'ish changes, so feel free to ignore them