Make FileManagerDialog::SelectFileImpl() properly accept simple filenames as default path.

chrome/browser/resources/file_manager/js/file_manager.js

 // Copyright (c) 2011 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.
 
 // Setting the src of an img to an empty string can crash the browser, so we
 // use an empty 1x1 gif instead.
 const EMPTY_IMAGE_URI = 'data:image/gif;base64,'
         + 'R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw%3D%3D';
 
 var g_slideshow_data = null;
@@ skipping 1256 matching lines @@
         foundRemovable = true;
       } else {  // Done enumerating, and we know the answer.
         this.changeDirectory(foundRemovable ? '/' : DOWNLOADS_DIRECTORY,
                              CD_NO_HISTORY);
       }
     }.bind(this));
   };
 
   FileManager.prototype.setupPath_ = function(path) {
     // Split the dirname from the basename.
-    var ary = path.match(/^(.*?)(?:\/([^\/]+))?$/);
+    var ary = path.match(/^(?:(.*)\/)?([^\/]*)$/);
     if (!ary) {
       console.warn('Unable to split default path: ' + path);
       self.changeDirectory('/', CD_NO_HISTORY);
       return;
     }
 
     var baseName = ary[1];
     var leafName = ary[2];
 
     var self = this;
@@ skipping 2294 matching lines @@
 
     if (msg) {
       console.log('no no no');
       this.alert.show(msg, onAccept);
       return false;
     }
 
     return true;
   };
 })();