Create a field test for sync sign in promo strings.

chrome/browser/resources/sync_promo.js

 // Copyright (c) 2011 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.
 
 // TODO(sail): Refactor options_page and remove this include.
 <include src="options/options_page.js"/>
 <include src="sync_setup_overlay.js"/>
 
 cr.define('sync_promo', function() {
   /**
@@ skipping 257 matching lines @@
   };
 
   SyncPromo.setPromoTitleVisible = function(visible) {
     SyncPromo.getInstance().setPromoTitleVisible_(visible);
   };
 
   SyncPromo.recordPageViewActions = function() {
     SyncPromo.getInstance().recordPageViewActions_();
   };
 
+  SyncPromo.populatePromoMessage = function(resName) {
+    SyncPromo.getInstance().populatePromoMessage_(resName);
+  };
+
   // Export
   return {
     SyncPromo: SyncPromo
   };
 });
 
 var OptionsPage = options.OptionsPage;
 var SyncSetupOverlay = sync_promo.SyncPromo;
 window.addEventListener('DOMContentLoaded', sync_promo.SyncPromo.initialize);
 window.addEventListener('beforeunload',
     sync_promo.SyncPromo.recordPageViewActions.bind(sync_promo.SyncPromo));