Measure usage metrics to prepare for adaptive fetching rates in M55

components/ntp_snippets/user_classifier.h

+// 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.
+
+#ifndef COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_
+#define COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace ntp_snippets {
+
+// Collects data about user usage patterns of content suggestions, computes
+// long-term user metrics locally using pref, reports the metrics to UMA,
+// classifies the users into discrete categories based on the metrics, and makes
+// the metrics and the classification available to other parts of the component.
+// TODO(jkrcal): Add the classification and the getters.

[Marc Treib, 2016/09/07 13:23:48]

nit: IMO the comment above should say only what the class actually does right
now; the TODO should mention what you plan on adding.

[jkrcal, 2016/09/07 14:19:08]

Done.

+class UserClassifier {
+ public:
+  // The provided |pref_service| may be nullptr in unit-tests.
+  explicit UserClassifier(PrefService* pref_service);
+  ~UserClassifier();
+
+  // Registers profile prefs for all metrics. Called from browser_prefs.cc.
+  static void RegisterProfilePrefs(PrefRegistrySimple* registry);
+
+  // When the user opens a new NTP - this indicates potential use of content
+  // suggestions.
+  void OnNTPOpened();
+  // When the content suggestions are shown to the user - in the current

[Bernhard Bauer, 2016/09/07 13:46:45]

Add empty lines before comment blocks?

[jkrcal, 2016/09/07 14:19:08]

Done.

+  // implementation when the user scrolls below the fold.
+  void OnSuggestionsShown();
+  // When the user clicks on some suggestions or on some "More" button.
+  void OnSuggestionsUsed();
+
+ private:
+  double UpdateMetric(const char* metric_pref_name,
+                      const char* last_time_pref_name,
+                      double default_metric_value);
+
+  double GetHoursSinceLastTime(const char* last_time_pref_name,
+                               double default_hours_since_last_time);
+  void SetLastTimeToNow(const char* last_time_pref_name);
+
+  PrefService* pref_service_;

[Bernhard Bauer, 2016/09/07 13:46:45]

DISALLOW_COPY_AND_ASSIGN

[jkrcal, 2016/09/07 14:19:08]

Done.

+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_