[web_dev_style] Changing :pseudo-element to ::pseudo-element to match

chrome/browser/resources/ntp4/footer_menu.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. */
 
 .footer-menu-button {
   -webkit-appearance: none;
   -webkit-padding-end: 15px;
   -webkit-padding-start: 9px;
   -webkit-transition: opacity 200ms;
   -webkit-transition-delay: 100ms;
@@ skipping 108 matching lines @@
   margin-top: 0.25em;
 }
 
 /* Used to add additional details to a section header */
 .footer-menu section h3 .details {
   color: rgb(151, 156, 160);
   font-style: italic;
   font-weight: normal;
 }
 
-.footer-menu section h3 .details:before {
+.footer-menu section h3 .details::before {
   content: '\2013';  /* En-dash character. */
   margin: 0 0.5em;
 }
 
 html[dir='rtl'] .footer-menu-item {
   background: no-repeat 100% 50%;
 }
 
 .recent-window {
   background-image: url('images/closed_window.png');
@@ skipping 18 matching lines @@
 .footer-menu-context-menu {
   /* Needs to be above .footer-menu. */
   z-index: 11;
 }
 
 .footer-menu hr {
   background-color: rgb(217, 217, 217);
   border: 0;
   height: 1px;
 }