Use HighDPI asset on about:flags

chrome/browser/resources/flags.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. */
 
 body {
   margin: 10px;
   min-width: 47em;
   /* Should match needs-restart.(height + padding-top + padding-bottom + 5) */
   padding-bottom: 65px;
 }
@@ skipping 10 matching lines @@
   /* 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 {
   -webkit-padding-start: 75px;
-  background: url('../../app/theme/flags_section.png') 0 20px no-repeat;
+  background: -webkit-image-set(
+      url('../../app/theme/default_100_percent/flags_section.png') 1x,

[Dan Beam, 2013/01/07 19:39:21]

if possible I'd like to use grit to autogenerate this for us like this -
https://codereview.chromium.org/11774004 - is there a functional difference?

+      url('../../app/theme/default_200_percent/flags_section.png') 2x)
+      0 20px no-repeat;
   display: inline;
   margin: 0;
   padding-bottom: 40px;
   padding-top: 40px;
 }
 
 html[dir=rtl] #header h1 {
-  background: url('../../app/theme/flags_section.png') right no-repeat;
+  background: -webkit-image-set(
+      url('../../app/theme/default_100_percent/flags_section.png') 1x,
+      url('../../app/theme/default_200_percent/flags_section.png') 2x)
+      right no-repeat;
 }
 
 h1 {
   font-size: 156%;
   font-weight: bold;
   margin: 0;
   padding: 0;
 }
 
 #blurb-container {
@@ skipping 106 matching lines @@
   /* If you change this, update body.padding-bottom */
   padding-top: 15px;
   position: fixed;
   width: 100%;
 }
 
 button {
   font-size: 104%;
 }