Not showing folders in the bottom pannel.

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 1735 matching lines @@
       selection.urls.push(entry.toURL());
 
       if (selection.iconType == null) {
         selection.iconType = this.getIconType(entry);
       } else if (selection.iconType != 'unknown') {
         var iconType = this.getIconType(entry);
         if (selection.iconType != iconType)
           selection.iconType = 'unknown';
       }
 
-      if (thumbnailCount < MAX_PREVIEW_THUMBAIL_COUNT) {
+      if (thumbnailCount < MAX_PREVIEW_THUMBAIL_COUNT && entry.isFile) {
         var thumbnail = this.renderThumbnailBox_(entry, true);
         thumbnail.style.zIndex = MAX_PREVIEW_THUMBAIL_COUNT + 1 - i;
         this.previewThumbnails_.appendChild(thumbnail);
         thumbnailCount++;
       }
 
       selection.totalCount++;
 
       if (entry.isFile) {
         selection.fileCount += 1;
@@ skipping 1969 matching lines @@
           });
       }, onError);
 
       function onError(err) {
         console.log('Error while checking free space: ' + err);
         setTimeout(doCheck, 1000 * 60);
       }
     }
   }
 })();