[Extensions] Update developerPrivate API to use base-64 data urls for icons

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 141 matching lines @@
   line-height: 32px;
 }
 
 .extension-list-item-wrapper {
   margin: 12px 0;
   padding: 12px;
 }
 
 .extension-list-item {
   background-repeat: no-repeat;
+  background-size: 48px 48px;
   display: -webkit-box;
   min-height: 48px;
 }
 
 .extension-list-item a {
   -webkit-margin-start: 0.5em;
   display: inline-block;
 }
 
 html[dir='rtl'] .extension-list-item {
@@ skipping 240 matching lines @@
 
 .sideload-wipeout-banner .page-banner-text {
   -webkit-padding-start: 8px;
   background-image: none;
 }
 
 .focus-row-active {
   background-color: rgba(0, 0, 0, .05);
   border-radius: 3px;
 }