Add UMA stats to track whitelist download latency.

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 141 matching lines @@
 </histogram>
 
 <histogram name="Autocheckout.WalletRequiredActions"
     enum="WalletRequiredActions">
   <summary>
     Measures the frequency of required user actions returned by the Google
     Online Wallet server.
   </summary>
 </histogram>
 
+<histogram name="Autocheckout.WhitelistDownloadDuration" units="ms">
+  <summary>
+    Measures time taken to download the Autocheckout whitelist file.
+  </summary>
+</histogram>
+
+<histogram name="Autocheckout.WhitelistDownloadDuration.Failed" units="ms">
+  <summary>
+    Measures time taken to download the Autocheckout whitelist file in case the
+    download was failed.
+  </summary>
+</histogram>
+
+<histogram name="Autocheckout.WhitelistDownloadDuration.Succeeded" units="ms">
+  <summary>
+    Measures time taken to download the Autocheckout whitelist file in case the
+    download was succeeded.
+  </summary>
+</histogram>
+
 <histogram name="Autofill.AddressSuggestionsCount">
   <summary>
     The number of address suggestions shown in the Autofill popup.
   </summary>
 </histogram>
 
 <histogram name="AutoFill.CCInfoBarAccepted">
   <obsolete>
     Deprecated as of 3/2011, replaced by Autofill.CreditCardInfoBar.
   </obsolete>
@@ skipping 5193 matching lines @@
 <fieldtrial name="SSLResumption">
   <group name="Resume_Handshake" label="Session Resumption"/>
   <group name="Full_Handshake" label="Full"/>
   <affected-histogram name="Net.SSL_Connection_Latency"/>
   <affected-histogram name="Net.SSL_Connection_Latency_Google"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>