Implement a site engagement score based on time-on-site.

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 60644a4a4e3f504721d10a8a2e0666eb635dac34..d6b82102c4fd9cc48b3e359d9d658f1beaa07694 100644
--- a/chrome/browser/engagement/site_engagement_service.h
+++ b/chrome/browser/engagement/site_engagement_service.h
@@ -31,8 +31,8 @@ class SiteEngagementScore {
   // The maximum number of points that can be accrued in one day.
   static const double kMaxPointsPerDay;
 
-  // The number of points given for a navigation.
-  static const double kNavigationPoints;
+  // The number of points given for user input (indicating time-on-site).
+  static const double kUserInputPoints;
 
   // Decaying works by removing a portion of the score periodically. This
   // constant determines how often that happens.
@@ -114,8 +114,9 @@ class SiteEngagementService : public KeyedService,
   explicit SiteEngagementService(Profile* profile);
   ~SiteEngagementService() override;
 
-  // Update the karma score of the origin matching |url| for user navigation.
-  void HandleNavigation(const GURL& url);
+  // Update the karma score of the origin matching |url| for time-on-site, based
+  // on user input.
+  void HandleUserInput(const GURL& url);
 
   // Overridden from SiteEngagementScoreProvider:
   int GetScore(const GURL& url) override;