Fixing race condition in prepearing thumbnails for the bottom panel.

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.col-resize * {
   cursor: col-resize !important;
 }
 
 /* Outer frame of the dialog. */
 body {
@@ skipping 697 matching lines @@
   pointer-events: none;
   position: absolute;
   z-index: 1;
 }
 
 .preview-thumbnails > * {
   -webkit-transition: all 180ms ease-in;
   -webkit-transition-delay: 300ms;
 }
 
-.preview-thumbnails:hover > .popup {
+.preview-thumbnails.has-zoom:hover > .popup {
   -webkit-transform: translate(0, 0) scale(1.0);
   opacity: 1;
   pointer-events: auto;
 }
 
-.preview-thumbnails:hover > .thumbnail {
+.preview-thumbnails.has-zoom:hover > .thumbnail {
   opacity: 0;
 }
 
 /* cr.ui.Table has a black focus border by default, which we don't want. */
 .detail-table:focus {
   border: 0;
 }
 
 /* Table splitter element */
 .table-header-splitter {
@@ skipping 550 matching lines @@
 }
 
 #no-search-results {
   bottom: 0;
   left: 0;
   padding: 10px;
   position: absolute;
   right: 0;
   top: 28px;  /* Leave room for the file list header. */
 }