Allow the site engagement service thresholds to be varied via field trial.

chrome/browser/engagement/site_engagement_service.h

 // Copyright 2015 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_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 #define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 
 #include <map>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "chrome/browser/engagement/site_engagement_metrics.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "ui/base/page_transition_types.h"
 
 namespace base {
 class DictionaryValue;
 class Clock;
 }
 
 class GURL;
 class Profile;
 
 class SiteEngagementScore {
  public:
-  // Keys used in the content settings dictionary.
-  static const char* kRawScoreKey;
-  static const char* kPointsAddedTodayKey;
-  static const char* kLastEngagementTimeKey;
-
   // The maximum number of points that are allowed.
   static const double kMaxPoints;
 
   // The maximum number of points that can be accrued in one day.
-  static const double kMaxPointsPerDay;
+  static double g_max_points_per_day;
 
   // The number of points given for navigations.
-  static const double kNavigationPoints;
+  static double g_navigation_points;
 
   // The number of points given for user input (indicating time-on-site).
-  static const double kUserInputPoints;
+  static double g_user_input_points;
 
   // Decaying works by removing a portion of the score periodically. This
   // constant determines how often that happens.
-  static const int kDecayPeriodInDays;
+  static int g_decay_period_in_days;
 
   // How much the score decays after every kDecayPeriodInDays.
-  static const double kDecayPoints;
+  static double g_decay_points;
+
+  // Update the default engagement settings via variations.
+  static void UpdateFromVariations();
 
   // The SiteEngagementService does not take ownership of |clock|. It is the
   // responsibility of the caller to make sure |clock| outlives this
   // SiteEngagementScore.
   SiteEngagementScore(base::Clock* clock,
                       const base::DictionaryValue& score_dict);
   ~SiteEngagementScore();
 
   double Score() const;
   void AddPoints(double points);
 
   // Returns true if the maximum number of points today has been added.
   bool MaxPointsPerDayAdded();
 
   // Updates the content settings dictionary |score_dict| with the current score
   // fields. Returns true if |score_dict| changed, otherwise return false.
   bool UpdateScoreDict(base::DictionaryValue* score_dict);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(SiteEngagementScoreTest, PartiallyEmptyDictionary);
+  FRIEND_TEST_ALL_PREFIXES(SiteEngagementScoreTest, PopulatedDictionary);
   friend class SiteEngagementScoreTest;
 
+  // Keys used in the content settings dictionary.
+  static const char* kRawScoreKey;
+  static const char* kPointsAddedTodayKey;
+  static const char* kLastEngagementTimeKey;
+
   // This version of the constructor is used in unit tests.
   explicit SiteEngagementScore(base::Clock* clock);
 
   // Determine the score, accounting for any decay.
   double DecayedScore() const;
 
   // The clock used to vend times. Enables time travelling in tests. Owned by
   // the SiteEngagementService.
   base::Clock* clock_;
 
@@ skipping 97 matching lines @@
   // origin's engagement score after an hour has elapsed triggers the next
   // upload.
   base::Time last_metrics_time_;
 
   base::WeakPtrFactory<SiteEngagementService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SiteEngagementService);
 };
 
 #endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_