Adding OOBE high DPI assets

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 69 matching lines @@
 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;
 }
 
 html[oobe=new] #login-header-bar #shutdown-button {
-  background-image: url('chrome://theme/IDR_ICON_POWER24_WHITE');
+  background-image: -webkit-image-set(
+      url('chrome://theme/IDR_ICON_POWER_WHITE') 1x,
+      url('chrome://theme/IDR_ICON_POWER_WHITE@2x') 2x);
 }
 
 #login-header-bar #add-user-button {
   background-image: url('chrome://theme/IDR_ICON_ADD_USER24');
   background-size: 24px;
 }
 
 html[oobe=new] #login-header-bar #add-user-button {
-  background-image: url('chrome://theme/IDR_ICON_ADD_USER24_WHITE');
+  background-image: -webkit-image-set(
+      url('chrome://theme/IDR_ICON_ADD_USER_WHITE') 1x,
+      url('chrome://theme/IDR_ICON_ADD_USER_WHITE@2x') 2x);
 }