[NTP Snippets] Report the share of the UI lang vs. the top non-UI lang

components/ntp_snippets/remote/ntp_snippets_fetcher.cc

 // Copyright 2016 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.
 
 #include "components/ntp_snippets/remote/ntp_snippets_fetcher.h"
 
 #include <cstdlib>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 527 matching lines @@
 
   params->ui_language.language_code = ISO639FromPosixLocale(locale_);
   params->ui_language.frequency =
       language_model_->GetLanguageFrequency(params->ui_language.language_code);
 
   std::vector<LanguageModel::LanguageInfo> top_languages =
       language_model_->GetTopLanguages();
   for (const LanguageModel::LanguageInfo& info : top_languages) {
     if (info.language_code != params->ui_language.language_code) {
       params->other_top_language = info;
+
+      // Report to UMA how important the UI language is.
+      DCHECK_GT(params->other_top_language.frequency, 0)
+          << "GetTopLanguages() should not return languages with 0 frequency";
+      float ratio_ui_in_both_languages = params->ui_language.frequency /
+                                         (params->ui_language.frequency +
+                                          params->other_top_language.frequency);
+      UMA_HISTOGRAM_PERCENTAGE(
+          "NewTabPage.Languages.UILanguageRatioInTwoTopLanguages",
+          ratio_ui_in_both_languages * 100);
       break;
     }
   }
 }
 
 void NTPSnippetsFetcher::FetchSnippetsNonAuthenticated() {
   // When not providing OAuth token, we need to pass the Google API key.
   GURL url(base::StringPrintf(kSnippetsServerNonAuthorizedFormat,
                               fetch_url_.spec().c_str(), api_key_.c_str()));
 
@@ skipping 225 matching lines @@
           interactive_request);
     case UserClassifier::UserClass::ACTIVE_SUGGESTIONS_CONSUMER:
       return request_throttler_active_suggestions_consumer_
           .DemandQuotaForRequest(interactive_request);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace ntp_snippets