Remove hard-coded font families in WebUI.

chrome/browser/resources/chromeos/provided_file_systems.css

 /* Copyright 2014 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 {
   background-color: rgba(0, 0, 0, 0.05);
-  font-family: sans-serif;
   font-size: 14px;
   margin: 20px;
 }
 
 #fileSystems,
 #requestEvents,
 #requestTimeline {
   background-color: white;
   box-shadow: 0 1px 2px 0 rgba(0, 0, 0, 0.2);
   margin-bottom: 20px;
@@ skipping 161 matching lines @@
 #requestEvents [data-request-type='READ_FILE'] span {
   background-color: royalblue;
   color: white;
 }
 
 #requestTimeline [data-state='rejected'],
 #requestEvents [data-error]:not([data-error='']) span {
   background-color: tomato;
   color: white;
 }