Use chrome_html structure for shared_resources and options2 page.

chrome/browser/resources/chromeos/login/header_bar.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.
  */
 
 #login-header-bar {
   -webkit-padding-after: 7px;
   bottom: 0;
   left: 0;
   position: absolute;
@@ skipping 13 matching lines @@
   opacity: 0.6;
   padding: 5px 8px;
   vertical-align: middle;
 }
 
 .header-bar-item {
   -webkit-padding-start: 15px;
   background-image: url('chrome://theme/IDR_DIVIDER_VERT');
   background-position: -2px center;
   background-repeat: no-repeat;
+  background-size: 15px;
   display: inline-block;
   height: 34px;
 }
 
 html[dir=rtl] .header-bar-item {
   background-position: right center;
 }
 
 .header-bar-item:first-child {
   -webkit-padding-start: 9px;
   background: none;
 }
 
 #login-header-bar #shutdown-button,
 #login-header-bar #add-user-button {
   -webkit-padding-start: 24px;
   background-position: left center;
   background-repeat: no-repeat;
 }
 
 html[dir=rtl] #login-header-bar #shutdown-button,
 html[dir=rtl] #login-header-bar #add-user-button {
   background-position: right center;
 }
 
 #login-header-bar #shutdown-button {
   background-image: url('chrome://theme/IDR_ICON_POWER24');
+  background-size: 24px;
 }
 
 #login-header-bar #add-user-button {
   background-image: url('chrome://theme/IDR_ICON_ADD_USER24');
+  background-size: 24px;
 }