When searching show spinner inplace of magnifying glass in the searchbox.

chrome/browser/resources/file_manager/css/file_manager.css

 /* 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. */
 
 html {
   height: 100%;
 }
 
 html.col-resize * {
   cursor: col-resize !important;
@@ skipping 445 matching lines @@
     url('../images/files/ui/2x/icon_search.png') 2x);
   background-position: 4px 4.5px;
   background-repeat: no-repeat;
   display: -webkit-box;
   height: 27px;
   margin-right: 10px;
   padding: 1px 6px 2px 23px;
   width: 150px;
 }
 
+.searching #search-box {
+  background-image: url('../images/common/spinner.svg');
+  background-size: 17px 17px;
+}
+
 #search-box:focus {
   border-color: rgb(77, 144, 254);
   outline: none;
   width: 240px;
 }
 
 #search-box,
 #filename-input-box input {
   border: 1px solid #BBB;
   border-radius: 2px;
@@ skipping 1041 matching lines @@
   height: 100%;
 }
 
 #list-container .table-header-cell:hover {
   background-color: #f2f2f2;
 }
 
 button:focus {
   outline-color: rgb(77, 144, 254);
 }