Remove hard-coded font families in WebUI.

chrome/browser/resources/contextual_search/promo.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.
 */
 @font-face {
   font-family: 'Roboto2';
   font-weight: 400;
   src: local('Roboto'), local('Roboto2-Regular'),
       url(/roboto.woff2) format('woff2'), url(/roboto.woff) format('woff');
 }
 
 body {
   color: #414141;
-  font-family: 'Roboto2', sans-serif;

[jungshik at Google, 2014/12/16 20:44:00]

Again, let's leave this alone because this file is importing a local version of
Roboto (see @font-face above) for now. 
This need to be cleaned up later.@font-face will not be necessary when we
cleaned it up. How about adding TODO comment about the clean-up? 

   margin: 0;
 }
 
 a {
   text-decoration: none;
 }
 
 a.colored-link {
   color: rgb(66, 133, 244);
 }
@@ skipping 76 matching lines @@
   margin-right: 24px;
 }
 
 #optin-label a {
   color: white;
 }
 
 #optout-label a {
   color: rgb(66, 133, 244);
 }