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

chrome/browser/engagement/site_engagement_service.h

Index: chrome/browser/engagement/site_engagement_service.h
diff --git a/chrome/browser/engagement/site_engagement_service.h b/chrome/browser/engagement/site_engagement_service.h
index 0e67b7193bb982ef6326824fa498f8ab7122e5e6..cee44500afd4d5780165787a81c16e0283b90299 100644
--- a/chrome/browser/engagement/site_engagement_service.h
+++ b/chrome/browser/engagement/site_engagement_service.h
@@ -28,24 +28,35 @@ class SiteEngagementScore {
   static const char* kPointsAddedTodayKey;
   static const char* kLastEngagementTimeKey;
 
+  // Keys used in the variations params.
+  static const char* kEngagementParams;
+  static const char* kMaxPointsPerDayParam;
+  static const char* kNavigationPointsParam;
+  static const char* kUserInputPointsParam;
+  static const char* kDecayPeriodInDaysParam;
+  static const char* kDecayPointsParam;

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

Do all these keys (and the content settings keys) need to be public?

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

@calamity: any thoughts on making all of these private? I believe that they're
accessed a lot in tests.

[calamity, 2015/10/01 08:41:19]

These are just the keys, not the values?

I don't think they're used in tests too much.

I support privatization of this sector.

[dominickn, 2015/10/01 09:04:22]

Done.

+
   // 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 gMaxPointsPerDay;
 
   // The number of points given for navigations.
-  static const double kNavigationPoints;
+  static double gNavigationPoints;
 
   // The number of points given for user input (indicating time-on-site).
-  static const double kUserInputPoints;
+  static double gUserInputPoints;
 
   // Decaying works by removing a portion of the score periodically. This
   // constant determines how often that happens.
-  static const int kDecayPeriodInDays;
+  static int gDecayPeriodInDays;
 
   // How much the score decays after every kDecayPeriodInDays.
-  static const double kDecayPoints;
+  static double gDecayPoints;

[calamity, 2015/10/01 08:41:19]

nit: g_decay_points and above to match majority of Chrome.

[calamity, 2015/10/06 03:52:40]

Ping?

You can do this quickly by running

sed -i 's/gDecayPoints/g_decay_points/g' `git diff --name-only @{u}`

etc

[dominickn, 2015/10/06 05:00:39]

Done.

+
+  // 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