[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(params->other_top_language.frequency > 0)

[Marc Treib, 2016/10/14 15:32:56]

DCHECK_GT

[jkrcal, 2016/10/14 16:34:15]

Done.

+          << "GetTopLanguages() should not return languages with 0 frequency";
+      float ratio_ui_to_other_top_language =
+          params->ui_language.frequency / params->other_top_language.frequency;

[Marc Treib, 2016/10/14 15:32:56]

Should this be "ui_freq / (ui_freq + other_freq)" ?

[jkrcal, 2016/10/14 16:34:15]

Well, I meant it as it was. Your suggestion actually makes the data more
standard an easier to interpret :) Done.

+      UMA_HISTOGRAM_COUNTS_1000(

[Alexei Svitkine (slow), 2016/10/14 15:30:15]

I think you probably want to use UMA_HISTOGRAM_PERCENT here. Otherwise, you'll
get an exponentially scaled set of buckets.

[jkrcal, 2016/10/14 16:34:15]

This is what I wanted because the result was not supposed to be on the range of
0-100. 
Together with the change of Marc above, I can make it PERCENT. Which makes more
sense.

+          "NewTabPage.Languages.UILanguageToOtherTopLanguageRatio",
+          ratio_ui_to_other_top_language * 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