Add high dpi reference for extension icon on incognito tab.

chrome/browser/resources/incognito_tab.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. */
 
 body {
   margin: 10px 8px;
 }
 
 .icon {
   -webkit-margin-end: 3px;
@@ skipping 20 matching lines @@
   padding: 10px;
 }
 
 .extensions-message {
   -webkit-padding-start: 39px;
   margin-top: 15px;
   position: relative;
 }
 
 .extension-icon {
+  content: -webkit-image-set(
+      url('../../app/theme/default_100_percent/extensions_section.png') 1x,
+      url('../../app/theme/default_200_percent/extensions_section.png') 2x);
+  display: inline-block;
   left: 0;
   margin-top: -15px;
   position: absolute;
   right: 0;
   top: 50%;
   width: 30px;
 }