Get rid of a couple references to IDR_WARNING

chrome/browser/resources/extensions/extensions.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.loading * {
   transition-duration: 0ms !important;
 }
 
 html:not(.focus-outline-visible)
 :enabled:focus:-webkit-any(input[type='checkbox'], input[type='radio']) {
@@ skipping 397 matching lines @@
 }
 
 /* Supervised users */
 
 .page:not(.profile-is-supervised) .profile-is-supervised-banner,
 .profile-is-supervised .more-extensions-link {
   display: none;
 }
 
 .profile-is-supervised-banner .page-banner-text {
-  background-image: url(chrome://theme/IDR_WARNING);
+  background-image: url(../../../../ui/webui/resources/images/warning.svg);
+  background-size: 18px;
 }
 
 /* Sideload Wipeout */
 
 .sideload-wipeout-learn-more {
   text-decoration: none;
 }
 
 .sideload-wipeout-banner .page-banner-text {
   -webkit-padding-start: 8px;
   background-image: none;
 }
 
 .extension-highlight {
   background-color: rgba(0, 0, 0, .05);
 }