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

ui/webui/resources/css/chrome_shared.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 holds CSS that should be shared, in theory, by all user-visible
  * chrome:// pages. */
 
 @import url(chrome://resources/css/text_defaults.css);
 @import url(i18n_process.css);
 @import url(widgets.css);
@@ skipping 20 matching lines @@
   margin: 0;
 }
 
 p {
   line-height: 1.8em;
 }
 
 h1,
 h2,
 h3 {
-  -webkit-user-select: none;
   font-weight: normal;
   /* Makes the vertical size of the text the same for all fonts. */
   line-height: 1;
+  user-select: none;
 }
 
 h1 {
   font-size: 1.5em;
 }
 
 h2 {
   font-size: 1.3em;
   margin-bottom: 0.4em;
 }
@@ skipping 44 matching lines @@
   direction: ltr;
 }
 
 /* WebKit does not honor alignment for text specified via placeholder attribute.
  * This CSS is a workaround. Please remove once WebKit bug is fixed.
  * https://bugs.webkit.org/show_bug.cgi?id=63367 */
 html[dir='rtl'] input.weakrtl::-webkit-input-placeholder,
 html[dir='rtl'] .weakrtl input::-webkit-input-placeholder {
   direction: rtl;
 }