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..8f2ae0289d1337c71c09719a8869767d4a0b3996 100644
--- a/chrome/browser/engagement/site_engagement_service.h
+++ b/chrome/browser/engagement/site_engagement_service.h
@@ -10,6 +10,7 @@
 #include "base/time/default_clock.h"
 #include "base/time/time.h"
 #include "components/keyed_service/core/keyed_service.h"
+#include "ui/base/page_transition_types.h"
 
 namespace base {
 class DictionaryValue;
@@ -31,9 +32,12 @@ 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.
+  // The number of points given for navigations.
   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.
   static const int kDecayPeriodInDays;
@@ -87,10 +91,10 @@ class SiteEngagementScoreProvider {
  public:
   // Returns a non-negative integer representing the engagement score of the
   // origin for this URL.
-  virtual int GetScore(const GURL& url) = 0;
+  virtual double GetScore(const GURL& url) = 0;
 
   // Returns the sum of engagement points awarded to all sites.
-  virtual int GetTotalEngagementPoints() = 0;
+  virtual double GetTotalEngagementPoints() = 0;
 };
 
 // Stores and retrieves the engagement score of an origin.
@@ -114,14 +118,20 @@ 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 navigation.
+  void HandleNavigation(const GURL& url, ui::PageTransition transition);
+
+  // 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;
-  int GetTotalEngagementPoints() override;
+  double GetScore(const GURL& url) override;
+  double GetTotalEngagementPoints() override;
 
  private:
+  void AddPoints(const GURL& url, double points);
+
   Profile* profile_;
 
   // The clock used to vend times.