Support extension highlighting on the extensions page.

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 * {
   -webkit-transition-duration: 0 !important;
 }
 
 /* Developer mode */
 
@@ skipping 257 matching lines @@
 }
 
 .extension-list-item:not(:hover) .trash:not(:focus) {
   opacity: 0;
 }
 
 .extension-list-item-wrapper.may-not-disable .trash {
   visibility: hidden;
 }
 
+.extension-highlight {
+  background: rgb(238, 238, 238);
+  background-position: auto;
+  background-repeat: auto;
+  border-radius: 3px;
+  padding: 5px 0 5px 5px;
+}
+
 .may-not-disable .optional-controls .optional-controls-disableable {
   display: none;
 }
 
 /* Managed mode */
 
 .page:not(.managed-mode) .managed-mode-banner {
   display: none;
 }
 
 .managed-mode .more-extensions-link {
   display: none;
 }