In case of search add "Searching..." string to the spinner in the center.

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

 // 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.
 
 function MockEventSource() {
   this.listeners_ = [];
 }
 
 /**
  * Add a listener.
@@ skipping 641 matching lines @@
       TAR_BZIP2_ARCHIVE_FILE_TYPE: 'Bzip2 compressed tar archive',
       TAR_GZIP_ARCHIVE_FILE_TYPE: 'Gzip compressed tar archive',
       PLAIN_TEXT_FILE_TYPE: 'Plain text file',
       PDF_DOCUMENT_FILE_TYPE: 'PDF document',
       WORD_DOCUMENT_FILE_TYPE: 'Word document',
       POWERPOINT_PRESENTATION_FILE_TYPE: 'PowerPoint presentation',
       EXCEL_FILE_TYPE: 'Excel spreadsheet',
 
       SEARCH_TEXT_LABEL: 'Search',
       SEARCH_NO_MATCHING_FILES: 'No files match <b>"$1"</b>',
+      SEARCH_SPINNER: 'Searching...',
 
       TIME_TODAY: 'Today, $1',
       TIME_YESTERDAY: 'Yesterday, $1',
 
       ALL_FILES_FILTER: 'All files',
 
       DEFAULT_ACTION_LABEL: '(default)',
       ASH: true,
       DETAIL_VIEW_TOOLTIP: 'List view',
       THUMBNAIL_VIEW_TOOLTIP: 'Thumbnail view',
@@ skipping 144 matching lines @@
     compare: function(a, b) {
       if (a > b) return 1;
       if (a < b) return -1;
       return 0;
     }
   };
 };
 
 return v8Intl;
 }());