Use OAuth2 token for sync

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 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.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 10474 matching lines @@
   </summary>
 </histogram>
 
 <histogram name="Sync.AuthServerRejectedTokenAgeShort" units="milliseconds">
   <summary>
     Age of auth tokens younger than one hour that were rejected by the sync
     server. Measured from the time they were created.
   </summary>
 </histogram>
 
+<histogram name="Sync.RefreshTokenAvailable" enum="BooleanSuccess">
+  <summary>
+    Whether OAuth2 refresh token was available at the time when
+    ProfileSyncService was starting backend.
+  </summary>
+</histogram>
+
 <histogram name="Tab.RestoreResult" enum="BooleanSuccess">
   <summary>
     When the browser restores a tab, whether the load was successful. Loads can
     fail for instance when there is no connectivity.
   </summary>
 </histogram>
 
 <histogram name="Tab.RestoreTime" units="ms">
   <summary>Load time for a successful tab restore.</summary>
 </histogram>
@@ skipping 7898 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>