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

chrome/browser/engagement/site_engagement_service.cc

Index: chrome/browser/engagement/site_engagement_service.cc
diff --git a/chrome/browser/engagement/site_engagement_service.cc b/chrome/browser/engagement/site_engagement_service.cc
index 087a82b301dbe19dfd41e56630dc619d9c4b7e43..0287a5ce2a9c418721f738bac3e0ed919a547ba4 100644
--- a/chrome/browser/engagement/site_engagement_service.cc
+++ b/chrome/browser/engagement/site_engagement_service.cc
@@ -8,6 +8,7 @@
 #include <cmath>
 
 #include "base/command_line.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/time/clock.h"
 #include "base/time/default_clock.h"
 #include "base/values.h"
@@ -17,6 +18,7 @@
 #include "chrome/common/chrome_switches.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
 #include "components/content_settings/core/common/content_settings_pattern.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_thread.h"
 #include "url/gurl.h"
 
@@ -66,16 +68,64 @@ scoped_ptr<base::DictionaryValue> GetScoreDictForOrigin(
 
 }  // namespace
 
+const double SiteEngagementScore::kMaxPoints = 100;
+double SiteEngagementScore::gMaxPointsPerDay = 5;
+double SiteEngagementScore::gNavigationPoints = 0.5;
+double SiteEngagementScore::gUserInputPoints = 0.05;
+int SiteEngagementScore::gDecayPeriodInDays = 7;
+double SiteEngagementScore::gDecayPoints = 5;
+
 const char* SiteEngagementScore::kRawScoreKey = "rawScore";
 const char* SiteEngagementScore::kPointsAddedTodayKey = "pointsAddedToday";
 const char* SiteEngagementScore::kLastEngagementTimeKey = "lastEngagementTime";
 
-const double SiteEngagementScore::kMaxPoints = 100;
-const double SiteEngagementScore::kMaxPointsPerDay = 5;
-const double SiteEngagementScore::kNavigationPoints = 0.5;
-const double SiteEngagementScore::kUserInputPoints = 0.05;
-const int SiteEngagementScore::kDecayPeriodInDays = 7;
-const double SiteEngagementScore::kDecayPoints = 5;
+const char* SiteEngagementScore::kEngagementParams = "SiteEngagementParams";
+const char* SiteEngagementScore::kMaxPointsPerDayParam = "max_points_per_day";
+const char* SiteEngagementScore::kNavigationPointsParam = "navigation_points";
+const char* SiteEngagementScore::kUserInputPointsParam = "user_input_points";
+const char* SiteEngagementScore::kDecayPeriodInDaysParam =
+    "decay_period_in_days";
+const char* SiteEngagementScore::kDecayPointsParam = "decay_points";
+
+// static
+void SiteEngagementScore::UpdateFromVariations() {
+  std::string max_points_per_day_param = variations::GetVariationParamValue(
+      kEngagementParams, kMaxPointsPerDayParam);
+  std::string navigation_points_param = variations::GetVariationParamValue(
+      kEngagementParams, kNavigationPointsParam);
+  std::string user_input_points_param = variations::GetVariationParamValue(
+      kEngagementParams, kUserInputPointsParam);
+  std::string decay_period_in_days_param = variations::GetVariationParamValue(
+      kEngagementParams, kDecayPeriodInDaysParam);
+  std::string decay_points_param = variations::GetVariationParamValue(
+      kEngagementParams, kDecayPointsParam);
+
+  if (!max_points_per_day_param.empty() && !navigation_points_param.empty() &&
+      !user_input_points_param.empty() && !decay_period_in_days_param.empty() &&
+      !decay_points_param.empty()) {
+    double max_points_per_day = 0;
+    double navigation_points = 0;
+    double user_input_points = 0;
+    int decay_period_in_days = 0;
+    double decay_points = 0;
+
+    if (base::StringToDouble(max_points_per_day_param, &max_points_per_day) &&
+        base::StringToDouble(navigation_points_param, &navigation_points) &&
+        base::StringToDouble(user_input_points_param, &user_input_points) &&
+        base::StringToInt(decay_period_in_days_param, &decay_period_in_days) &&
+        base::StringToDouble(decay_points_param, &decay_points) &&
+        max_points_per_day >= navigation_points &&
+        max_points_per_day >= user_input_points && navigation_points >= 0 &&
+        user_input_points >= 0 && decay_period_in_days > 0 &&
+        decay_points >= 0) {
+      gMaxPointsPerDay = max_points_per_day;
+      gNavigationPoints = navigation_points;
+      gUserInputPoints = user_input_points;
+      gDecayPeriodInDays = decay_period_in_days;
+      gDecayPoints = decay_points;
+    }
+  }
+}
 
 SiteEngagementScore::SiteEngagementScore(
     base::Clock* clock,
@@ -107,7 +157,7 @@ void SiteEngagementScore::AddPoints(double points) {
   }
 
   double to_add =
-      std::min(kMaxPoints - raw_score_, kMaxPointsPerDay - points_added_today_);
+      std::min(kMaxPoints - raw_score_, gMaxPointsPerDay - points_added_today_);
   to_add = std::min(to_add, points);
 
   points_added_today_ += to_add;
@@ -122,7 +172,7 @@ bool SiteEngagementScore::MaxPointsPerDayAdded() {
     return false;
   }
 
-  return points_added_today_ == kMaxPointsPerDay;
+  return points_added_today_ == gMaxPointsPerDay;
 }
 
 bool SiteEngagementScore::UpdateScoreDict(base::DictionaryValue* score_dict) {
@@ -168,8 +218,8 @@ double SiteEngagementScore::DecayedScore() const {
   if (days_since_engagement < 0)
     return raw_score_;
 
-  int periods = days_since_engagement / kDecayPeriodInDays;
-  double decayed_score = raw_score_ - periods * kDecayPoints;
+  int periods = days_since_engagement / gDecayPeriodInDays;
+  double decayed_score = raw_score_ - periods * gDecayPoints;
   return std::max(0.0, decayed_score);
 }
 
@@ -200,7 +250,7 @@ void SiteEngagementService::HandleNavigation(const GURL& url,
                                              ui::PageTransition transition) {
   SiteEngagementMetrics::RecordEngagement(
       SiteEngagementMetrics::ENGAGEMENT_NAVIGATION);
-  AddPoints(url, SiteEngagementScore::kNavigationPoints);
+  AddPoints(url, SiteEngagementScore::gNavigationPoints);
 
   if (clock_->Now() - last_metrics_time_ >= metrics_interval)
     RecordMetrics();
@@ -210,7 +260,7 @@ void SiteEngagementService::HandleUserInput(
     const GURL& url,
     SiteEngagementMetrics::EngagementType type) {
   SiteEngagementMetrics::RecordEngagement(type);
-  AddPoints(url, SiteEngagementScore::kUserInputPoints);
+  AddPoints(url, SiteEngagementScore::gUserInputPoints);
 
   if (clock_->Now() - last_metrics_time_ >= metrics_interval)
     RecordMetrics();
@@ -283,6 +333,7 @@ void SiteEngagementService::AddPoints(const GURL& url, double points) {
 
 void SiteEngagementService::AfterStartupTask() {
   CleanupEngagementScores();
+  SiteEngagementScore::UpdateFromVariations();

[benwells, 2015/10/02 01:37:42]

I think this is the wrong place for this, as there will be some delay between
the service being created and the startup task happening.

You should probably do it in the constructor instead.

I think it would also be good to ensure it only happens once, maybe with another
global variable. Doing it multiple times (i.e. for every profile) is probably ok
but it just feels like something waiting to go wrong. (yes I know the banner
stuff does it like this but that made me a bit uneasy too).

[dominickn, 2015/10/02 06:29:05]

Done.

   RecordMetrics();
 }