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

ui/webui/resources/css/widgets.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. */
 
 /* This file defines styles for form controls. The order of rule blocks is
  * important as there are some rules with equal specificity that rely on order
  * as a tiebreaker. These are marked with OVERRIDE. */
 
 @import url(action_link.css);
 
 /* Default state **************************************************************/
 
 :-webkit-any(button,
              input[type='button'],
              input[type='submit']):not(.custom-appearance),
 select,
 input[type='checkbox'],
 input[type='radio'] {
   -webkit-appearance: none;
-  -webkit-user-select: none;
   background-image: -webkit-linear-gradient(#ededed, #ededed 38%, #dedede);
   border: 1px solid rgba(0, 0, 0, 0.25);
   border-radius: 2px;
   box-shadow: 0 1px 0 rgba(0, 0, 0, 0.08),
       inset 0 1px 2px rgba(255, 255, 255, 0.75);
   color: #444;
   font: inherit;
   margin: 0 1px 0 0;
   outline: none;
   text-shadow: 0 1px 0 rgb(240, 240, 240);
+  user-select: none;
 }
 
 :-webkit-any(button,
              input[type='button'],
              input[type='submit']):not(.custom-appearance),
 select {
   min-height: 2em;
   min-width: 4em;
   padding-top: 1px;
   padding-bottom: 1px;
@@ skipping 70 matching lines @@
 input[type='search'] {
   -webkit-appearance: textfield;
   /* NOTE: Keep a relatively high min-width for this so we don't obscure the end
    * of the default text in relatively spacious languages (i.e. German). */
   min-width: 160px;
 }
 
 /* Checked ********************************************************************/
 
 input[type='checkbox']:checked::before {
-  -webkit-user-select: none;
   background-image: url(../images/check.png);
   background-size: 100% 100%;
   content: '';
   display: block;
   height: 100%;
+  user-select: none;
   width: 100%;
 }
 
 input[type='radio']:checked::before {
   background-color: #666;
   border-radius: 100%;
   bottom: 3px;
   content: '';
   display: block;
   left: 3px;
@@ skipping 112 matching lines @@
  *
  *   <div class="checkbox">
  *     <label>
  *       <input type="checkbox"></input>
  *       <span>
  *     </label>
  *   </div>
  */
 
 :-webkit-any(.checkbox, .radio) label {
-  -webkit-user-select: none;
   /* Don't expand horizontally: <http://crbug.com/112091>. */
   align-items: center;
   display: inline-flex;
   padding-bottom: 7px;
   padding-top: 7px;
+  user-select: none;
 }
 
 :-webkit-any(.checkbox, .radio) label input {
   flex-shrink: 0;
 }
 
 :-webkit-any(.checkbox, .radio) label input ~ span {
   -webkit-margin-start: 0.6em;
   /* Make sure long spans wrap at the same horizontal position they start. */
   display: block;
 }
 
 :-webkit-any(.checkbox, .radio) label:hover {
   color: black;
 }
 
 label > input:disabled:-webkit-any([type='checkbox'], [type='radio']) ~ span {
   color: #999;
 }
 
 extensionview {
   display: inline-block;
   height: 300px;
   width: 300px;
 }