HiDPI asset for the help bubble on about:memory

chrome/browser/resources/shared/css/about_memory.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 {
   font-size: 84%;
   margin: 0;
   min-width: 45em;
   padding: 0.75em;
 }
@@ skipping 240 matching lines @@
   text-align: center;
 }
 
 table.list#browserComparison .name {
   background-position: 5px center;
   background-repeat: no-repeat;
   padding-left: 25px;
 }
 
 div.help {
-  background: url('../images/help.gif') center bottom no-repeat;
+  background: url('../images/help.png') center bottom no-repeat;
   display: inline-block;
   height: 14px;
   margin: -1px 0;
   opacity: 0.33;
   width: 14px;
 }
 
 div.help:hover {
   opacity: 1;
 }
@@ skipping 17 matching lines @@
 
 #helpTooltip p {
   margin: 0.6em 0;
 }
 
 div.otherbrowsers {
   font-size: 84%;
   text-align: center;
   width: 100%;
 }