Add the new UMA key 'Translate.LocalesOnDisabledByPrefs'.

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 8955 matching lines @@
 </histogram>
 
 <histogram name="Translate.LanguageVerification"
     enum="TranslateLanguageVerification">
   <summary>
     For each page load, measures whether the provided Content-Language header
     matches the language determined by CLD.
   </summary>
 </histogram>
 
+<histogram name="Translate.LocalesOnDisabledByPrefs" enum="LanguageCode">
+  <summary>
+    Logs the user locale when the Translate feature is disabled by the user.
+    This is recorded each time a webpage is loaded and prefs for translation is
+    checked. This allows us to investigate the correlation between the user
+    locale and the usage rates of the Translate.
+  </summary>
+</histogram>
+
 <histogram name="Translate.PageScheme" enum="TranslateScheme">
   <summary>Counts translation target page schemes.</summary>
 </histogram>
 
 <histogram name="Translate.ShowErrorInfobar" enum="TranslateError">
   <summary>
     Chrome Translate shows an error infobar when an error happens on translation
     and the infobar message depends on what kind of error happens. This metric
     counts how often each error message is shown.
   </summary>
@@ skipping 6788 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>