Remove hard-coded font families in WebUI.

chrome/browser/resources/net_internals/events_view.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.
  */
 
 #events-view-filter-box {
   background: #efefef;
   border-bottom: 1px solid #aaa;
-  font-family: sans-serif;
   font-size: 75%;
   overflow: hidden;
   padding: 5px;
   white-space: nowrap;
 }
 
 #events-view-filter-box input {
   width: 100%;
 }
 
@@ skipping 78 matching lines @@
   color: rgb(112, 0, 112);
 }
 
 #events-view-source-list-tbody .source-ipv6-probe-job {
   color: rgb(235, 0, 0);
 }
 
 #events-view-source-list-tbody .source-none {
   color: rgb(235, 0, 0);
 }