[Sync] Fix USS type status counters.

components/sync/driver/resources/about.js

 // 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.
 
 cr.define('chrome.sync.about_tab', function() {
   // Contains the latest snapshot of sync about info.
   chrome.sync.aboutInfo = {};
 
   function highlightIfChanged(node, oldVal, newVal) {
     function clearHighlight() {
@@ skipping 23 matching lines @@
 
   function onAboutInfoCountersUpdated(e) {
     var details = e.details;
 
     var modelType = details.modelType;
     var counters = details.counters;
 
     var type_status_array = chrome.sync.aboutInfo.type_status;
     type_status_array.forEach(function(row) {
       if (row.name == modelType) {
-        row.num_entries = counters.numEntriesAndTombstones;
-        row.num_live = counters.numEntries;
+        // There are three types of counters, only "status" counters have these
+        // fields. Keep the old values if updated fields are not present.
+        if (counters.numEntriesAndTombstones) {
+          row.num_entries = counters.numEntriesAndTombstones;
+        }
+        if (counters.numEntries) {
+          row.num_live = counters.numEntries;
+        }
       }
     });
     jstProcess(
         new JsEvalContext({ type_status: type_status_array }),
         $('typeInfo'));
   }
 
   /**
    * Helper to determine if an element is scrolled to its bottom limit.
    * @param {Element} elem element to check
@@ skipping 151 matching lines @@
 
   return {
     onLoad: onLoad,
     addExpandListener: addExpandListener,
     highlightIfChanged: highlightIfChanged
   };
 });
 
 document.addEventListener(
     'DOMContentLoaded', chrome.sync.about_tab.onLoad, false);