Remove hard-coded font families in WebUI.

chrome/browser/resources/about_sys/about_sys.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.
  */
 
 #anchor {
   display: none;
 }
 
 body {
-  font-family: Arial, Helvetica, sans-serif;
   font-size: 84%;
   margin: 0;
   min-width: 45em;
   padding: 0.75em;
 }
 
 .global-button {
   margin: 1px 3px 0 3px;
 }
 
@@ skipping 141 matching lines @@
 }
 
 .number-expanded .stat-value {
   display: auto;
 }
 
 #status {
   color: rgb(255, 0, 0);
   margin: .5em 0;
 }