Replace extensions icon with MD icon.

chrome/browser/resources/components.css

 /* Copyright 2013 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;
   min-width: 47em;
 }
 
 a {
   color: blue;
   font-size: 103%;
 }
 
 #header {
   -webkit-padding-start: 0;
+  background: url(../../../ui/webui/resources/images/extension.svg)
+      left center / 48px no-repeat;
   box-sizing: border-box;
   margin-bottom: 1.05em;
-  /* 67px is the height of the header's background image. */
-  min-height: 67px;
   overflow: hidden;
-  padding-bottom: 20px;
-  padding-top: 20px;
   position: relative;
 }
 
-#header > h1 {
-  background: -webkit-image-set(
-      url(../../app/theme/default_100_percent/common/extensions_section.png) 1x,
-      url(../../app/theme/default_200_percent/common/extensions_section.png) 2x)
-      0 20px no-repeat;
-  display: inline;
-  margin: 0;
-  padding-bottom: 40px;
-  padding-left: 75px;
-  padding-top: 40px;
+html[dir=rtl] #header {
+  background-position-x: right;
 }
 
-html[dir=rtl] #header > h1 {
-  background: -webkit-image-set(
-      url(../../app/theme/default_100_percent/common/extensions_section.png) 1x,
-      url(../../app/theme/default_200_percent/common/extensions_section.png) 2x)
-      right no-repeat;
-  padding-left: 0;
-  padding-right: 95px;
+#header h1 {
+  -webkit-padding-start: 51px;
+  line-height: 48px;
 }
 
 h1 {
   font-size: 156%;
   font-weight: bold;
   margin: 0;
   padding: 0;
 }
 
 #disabled-container {
@@ skipping 198 matching lines @@
   margin-top: 0.2em;
 }
 
 .always-allow {
   -webkit-margin-start: 30px;
 }
 
 button {
   font-size: 104%;
 }