Translate: adopt html lang attribute if valid value is provided

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 8932 matching lines @@
   <summary>Tracks touchpad ThreeFingerSwipe setting on startup.</summary>
 </histogram>
 
 <histogram name="Translate.CaptureText" units="milliseconds">
   <summary>
     The time spent capturing plain text from the DOM. This is reported by
     ChromeRenderViewObserver when a page is loaded completely.
   </summary>
 </histogram>
 
-<histogram name="Translate.ContentLanguage" enum="TranslateContentLanguage">
+<histogram name="Translate.ContentLanguage" enum="TranslateLanguage">
   <summary>
     A page may provide a Content-Language HTTP header or a META tag. For each
     page load, measures whether the Content-Language header exists and is valid.
   </summary>
 </histogram>
 
+<histogram name="Translate.HtmlLang" enum="TranslateLanguage">
+  <summary>
+    A page may provide a lang attribute in html tag. For each page load,
+    measures whether the lang attribute exists and is valid.
+  </summary>
+</histogram>
+
 <histogram name="Translate.InitiationStatus" enum="TranslateInitiationStatus">
   <summary>
     The reason why Chrome decided to perform the next action (e.g., to show
     infobar, to translate a page without any prompting, and so on) when Chrome
     Translate is ready to translate a page.
   </summary>
 </histogram>
 
 <histogram name="Translate.LanguageVerification"
     enum="TranslateLanguageVerification">
@@ skipping 5096 matching lines @@
   </int>
   <int value="4" label="NO_TP_PRESENT_TP_EXPECTED_RESUME">
     Built-in touchpad not detected at resume time on a device with built-in
     touchpad (touchpad failure at resume time)
   </int>
   <int value="5" label="TP_PRESENT_TP_EXPECTED_RESUME">
     Built-in touchpad detected at resume time on a device with built-in touchpad
   </int>
 </enum>
 
-<enum name="TranslateContentLanguage" type="int">
-  <int value="0" label="No Content-Language"/>
-  <int value="1" label="Valid Content-Language"/>
-  <int value="2" label="Invalid Content-Language"/>
-</enum>
-
 <enum name="TranslateError" type="int">
   <int value="0" label="No error"/>
   <int value="1" label="Network error"/>
   <int value="2" label="Initialization error"/>
   <int value="3" label="Unknown language"/>
   <int value="4" label="Unsupported language"/>
   <int value="5" label="Identical language"/>
   <int value="6" label="Translation error"/>
 </enum>
 
 <enum name="TranslateInitiationStatus" type="int">
   <int value="0" label="Completely disabled by prefs"/>
   <int value="1" label="Completely disabled by switch"/>
   <int value="2" label="Disabled by user configuration"/>
   <int value="3" label="Unsupported Language"/>
   <int value="4" label="Unsupported URL"/>
   <int value="5" label="Do nothing for similar languages"/>
   <int value="6" label="Do nothing for accepted languages"/>
   <int value="7" label="Auto translation by user configuration"/>
   <int value="8" label="Auto translation by linked from a translated page"/>
   <int value="9" label="Show infobar"/>
 </enum>
 
+<enum name="TranslateLanguage" type="int">
+  <int value="0" label="No language code"/>
+  <int value="1" label="Valid language code"/>
+  <int value="2" label="Invalid language code"/>
+</enum>
+
 <enum name="TranslateLanguageVerification" type="int">
   <int value="0" label="CLD is disabled"/>
   <int value="1" label="No Content-Language"/>
   <int value="2" label="CLD can not determine a language"/>
   <int value="3" label="CLD agrees with Content-Language"/>
   <int value="4" label="CLD disagrees with Content-Language"/>
 </enum>
 
 <enum name="TranslateScheme" type="int">
   <int value="0" label="http"/>
@@ skipping 1697 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>