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 12a9879123b851530a5a751d305e1a055cb77824..30fff80092c54dffcf76499a6b06be844e9602cd 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/values.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.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 "url/gurl.h"
 
 namespace {
@@ -57,12 +59,60 @@ const char* SiteEngagementScore::kRawScoreKey = "rawScore";
 const char* SiteEngagementScore::kPointsAddedTodayKey = "pointsAddedToday";
 const char* SiteEngagementScore::kLastEngagementTimeKey = "lastEngagementTime";
 
+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";
+
 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;
+double SiteEngagementScore::gMaxPointsPerDay = 5;
+double SiteEngagementScore::gNavigationPoints = 0.5;
+double SiteEngagementScore::gUserInputPoints = 0.05;
+int SiteEngagementScore::gDecayPeriodInDays = 7;
+double SiteEngagementScore::gDecayPoints = 5;
+
+// static
+void SiteEngagementScore::UpdateFromVariations() {

[benwells, 2015/09/29 00:40:31]

Should something be calling this?

[dominickn, 2015/09/29 00:52:30]

It will once calamity's clean up CL lands. Then I will rebase this CL on that,
calling UpdateFromVariations() in a common init method that will clean up dead
scores, update from variations, and log UMA.

[benwells, 2015/09/29 01:10:44]

OK. Functions overwriting global variables feel weird, so I'm interested in
seeing where this is called. Ideally it will just be called once.

I'll wait to see how it is called before reviewing...

+  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,
@@ -94,7 +144,7 @@ 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;
@@ -109,7 +159,7 @@ bool SiteEngagementScore::MaxPointsPerDayAdded() {
     points_added_today_ = 0;
   }
 
-  return points_added_today_ == kMaxPointsPerDay;
+  return points_added_today_ == gMaxPointsPerDay;
 }
 
 bool SiteEngagementScore::UpdateScoreDict(base::DictionaryValue* score_dict) {
@@ -155,8 +205,8 @@ 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);
 }
 
@@ -181,11 +231,11 @@ SiteEngagementService::~SiteEngagementService() {
 
 void SiteEngagementService::HandleNavigation(const GURL& url,
                                              ui::PageTransition transition) {
-  AddPoints(url, SiteEngagementScore::kNavigationPoints);
+  AddPoints(url, SiteEngagementScore::gNavigationPoints);
 }
 
 void SiteEngagementService::HandleUserInput(const GURL& url) {
-  AddPoints(url, SiteEngagementScore::kUserInputPoints);
+  AddPoints(url, SiteEngagementScore::gUserInputPoints);
 }
 
 double SiteEngagementService::GetScore(const GURL& url) {