Making UserClassifier configurable by variation parameters

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_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/time/time.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, and reports the metrics to UMA.
 // Based on these lon-term user metrics, it classifies the user in a UserClass.

[Marc Treib, 2016/09/22 12:29:06]

s/lon-term/long-term/

[jkrcal, 2016/09/22 13:26:15]

Done.

 class UserClassifier {
  public:
   // Enumeration listing user classes
   enum class UserClass {
     RARE_NTP_USER,
     ACTIVE_NTP_USER,
     ACTIVE_SUGGESTIONS_CONSUMER,
   };
 
   // For estimating the average length of the intervals between two successive
@@ skipping 53 matching lines @@
   // return 0.
   double GetHoursSinceLastTime(Metric metric) const;
   bool HasLastTime(Metric metric) const;
   void SetLastTimeToNow(Metric metric);
 
   double GetMetricValue(Metric metric) const;
   void SetMetricValue(Metric metric, double metric_value);
   void ClearMetricValue(Metric metric);
 
   PrefService* pref_service_;
+
+  // Params of the metric.
   const double discount_rate_per_hour_;
+  const double min_hours_;
+  const double max_hours_;
+
+  // Params of the classification.
+  const double active_consumer_scrolls_at_least_once_per_hours_;
+  const double active_consumer_opens_ntp_at_least_once_per_hours_;

[Marc Treib, 2016/09/22 12:29:06]

I first wanted to say "s/consumer/user/ to be consistent with the enum", but
this actually described the most-active user class ("active consumer"). I find
that a bit confusing - any reason for introducing another requirement?
Intuitively, the scroll-below-the-fold rate should be sufficient, no?

[jkrcal, 2016/09/22 13:26:15]

Well, I wanted to be on the safe side and have more knobs to control things. You
are right, this is unnecessary complexity.

When we later see that other ways to classify are absolutely necessary, we might
still be able to merge it in M55 Beta. Anyway, classification of active
consumers is not that crucial (as classification of rare users).

+  const double rare_user_opens_ntp_at_most_once_per_hours_;
 
   DISALLOW_COPY_AND_ASSIGN(UserClassifier);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_USER_CLASSIFIER_H_