Drop the -webkit prefix from user-select CSS rule in ui/.

ui/webui/resources/css/dialogs.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. */
 
 .cr-dialog-container {
   -webkit-box-align: center;
   -webkit-box-pack: center;
   -webkit-transition: opacity 250ms linear;
-  -webkit-user-select: none;
   display: -webkit-box;
   height: 100%;
   left: 0;
   overflow: hidden;
   position: absolute;
   top: 0;
+  user-select: none;
   width: 100%;
   z-index: 9999;
 }
 
 .cr-dialog-frame {
   -webkit-box-orient: vertical;
   -webkit-box-shadow: 5px 5px 5px rgba(100, 100, 100, 0.5);
   background-color: white;
   border: 1px solid rgba(0, 0, 0, 0.3);
   border-radius: 3px;
@@ skipping 111 matching lines @@
   width: 44px;
 }
 
 .cr-dialog-close:hover {
   background-image: url(chrome://theme/IDR_CLOSE_DIALOG_H);
 }
 
 .cr-dialog-close:active {
   background-image: url(chrome://theme/IDR_CLOSE_DIALOG_P);
 }