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

chrome/browser/resources/bookmark_manager/css/bmm.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,
 body {
   cursor: default;
   height: 100%;
   margin: 0;
   overflow: hidden;
@@ skipping 58 matching lines @@
   background-position: 100% 50%;
 }
 
 list > .folder > .label {
   background-image: -webkit-image-set(
       url('../../../../../ui/resources/default_100_percent/common/folder_closed.png') 1x,
       url('../../../../../ui/resources/default_200_percent/common/folder_closed.png') 2x);
 }
 
 /* We need to ensure that even empty labels take up space */
-list > * > .label:empty:after,
-list > * > .url:empty:after {
+list > * > .label:empty::after,
+list > * > .url:empty::after {
   content: ' ';
   white-space: pre;
 }
 
-list > .folder > .url:empty:after {
+list > .folder > .url:empty::after {
   content: '';
 }
 
 list > * > button {
   -webkit-transition: opacity 150ms;
   background: #fff -webkit-canvas(drop-down-arrow) no-repeat center center;
   border: 1px solid hsl(214, 91%, 85%);
   border-radius: 3px;
   bottom: 1px;
   display: none;
@@ skipping 241 matching lines @@
 
   list [editing] input,
   .tree-item [editing] input {
     padding: 3px 0;
   }
 
   .tree-row .expand-icon {
     top: 6px;
   }
 }