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

components/ntp_snippets/remote/ntp_snippets_fetcher.cc

Index: components/ntp_snippets/remote/ntp_snippets_fetcher.cc
diff --git a/components/ntp_snippets/remote/ntp_snippets_fetcher.cc b/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
index 8e577878ffa620df986580aaed386f777fdc85f4..526960cb95d2be43805c4177bd10f6ee7f9447d0 100644
--- a/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
+++ b/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
@@ -545,6 +545,16 @@ void NTPSnippetsFetcher::SetUpCommonFetchingParameters(
   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;
     }
   }