Record language usage as UMA histograms.

chrome/browser/language_usage_metrics.h

+// Copyright (c) 2011 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.
+
+#ifndef CHROME_BROWSER_LANGUAGE_USAGE_METRICS_H_
+#define CHROME_BROWSER_LANGUAGE_USAGE_METRICS_H_
+#pragma once
+
+#include <set>
+#include <string>
+
+#include "base/gtest_prod_util.h"
+#include "third_party/cld/languages/public/languages.h"
+
+// Methods to record language usage as UMA histograms.
+// Language codes are defined in third_party/cld/languages/proto/languages.pb.h
+class LanguageUsageMetrics {
+

[Yusuke Sato, 2011/07/13 06:52:06]

nit: unnecessary vertical space?

[Yuzo, 2011/07/13 11:30:20]

Done.

+ public:
+  // Records accept languages as a UMA histogram. |accept_languages| is a
+  // case-insensitive comma-separated list of languages/locales of either xx or
+  // xx-YY format where xx is iso-639 language code and YY is iso-3166 country
+  // code. Country code is ignored. That is, xx and Xx-YY are considered

[Yusuke Sato, 2011/07/13 06:52:06]

s/Xx/xx/ ?

[Yusuke Sato, 2011/07/13 06:52:06]

Your implementation seems to handle xx_YY case as well. If so, please update the
doc.

[Yuzo, 2011/07/13 11:30:20]

Done.

[Yuzo, 2011/07/13 11:30:20]

It was intentional to express the case-insensitive'ness.
Changed to XX to avoid confusion.

+  // identical and recorded once.
+  static void RecordAcceptLanguages(const std::string& accept_languages);
+
+  // Records the application language as a UMA histogram. |application_locale|
+  // is a case-insensitive locale string of either xx or xx-YY format. Only the

[Yusuke Sato, 2011/07/13 06:52:06]

ditto.

[Yuzo, 2011/07/13 11:30:20]

Done.

+  // language part (xx in the example) is considered.
+  static void RecordApplicationLanguage(const std::string& application_locale);
+
+ private:
+  // This class must not be instantiated.
+  LanguageUsageMetrics() {}

[Yusuke Sato, 2011/07/13 06:52:06]

I believe you can omit the implementation, '{}', in this case.

 LanguageUsageMetrics();

[Yuzo, 2011/07/13 11:30:20]

Done.

+
+  // Parses |accept_languages| and returns a set of language codes in
+  // |languages|.
+  static void ParseAcceptLanguages(const std::string& accept_languages,
+                                   std::set<Language>* languages);
+
+  // Parses |locale| and returns the language code.

[Yusuke Sato, 2011/07/13 06:52:06]

Please mention the error return.

[Yuzo, 2011/07/13 11:30:20]

Done.

+  static Language ToLanguage(const std::string& locale);
+
+  FRIEND_TEST_ALL_PREFIXES(LanguageUsageMetricsTest, ParseAcceptLanguages);
+  FRIEND_TEST_ALL_PREFIXES(LanguageUsageMetricsTest, ToLanguage);
+};
+
+#endif  // CHROME_BROWSER_LANGUAGE_USAGE_METRICS_H_