Implement an observer interface for the site engagement service.

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 1d733322e887cced1264f0a6ac062984c06b8a99..1c0d9857d2935ad3deea2c5fe919e5f00e726122 100644
--- a/chrome/browser/engagement/site_engagement_service.h
+++ b/chrome/browser/engagement/site_engagement_service.h
@@ -12,8 +12,10 @@
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
 #include "base/time/time.h"
 #include "chrome/browser/engagement/site_engagement_metrics.h"
+#include "chrome/browser/engagement/site_engagement_observer.h"
 #include "components/history/core/browser/history_service_observer.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "ui/base/page_transition_types.h"
@@ -109,6 +111,7 @@ class SiteEngagementService : public KeyedService,
   double GetTotalEngagementPoints() const override;
 
  private:
+  friend class SiteEngagementObserver;
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, CheckHistograms);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, CleanupEngagementScores);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, ClearHistoryForURLs);
@@ -120,6 +123,7 @@ class SiteEngagementService : public KeyedService,
                            CleanupOriginsOnHistoryDeletion);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, IsBootstrapped);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, EngagementLevel);
+  FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, Observers);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, ScoreDecayHistograms);
   FRIEND_TEST_ALL_PREFIXES(AppBannerSettingsHelperTest, SiteEngagementTrigger);
 
@@ -139,6 +143,9 @@ class SiteEngagementService : public KeyedService,
   // Returns the median engagement score of all recorded origins.
   double GetMedianEngagement(const std::map<GURL, double>& score_map) const;
 
+  // Returns the minimum engagement score corresponding to |level|.
+  double GetScoreForEngagementLevel(EngagementLevel level) const;
+
   // Update the engagement score of the origin matching |url| for media playing.
   // The points awarded are discounted if the media is being played in a non-
   // visible tab.
@@ -172,6 +179,10 @@ class SiteEngagementService : public KeyedService,
     bool expired,
     const history::OriginCountAndLastVisitMap& remaining_origin_counts);
 
+  // Add and remove observers of this service.
+  void AddObserver(SiteEngagementObserver* observer);
+  void RemoveObserver(SiteEngagementObserver* observer);
+
   // Resets the engagement score for |url| to |score|, and sets the last
   // engagement time and last shortcut launch time (if it is non-null) to
   // |updated_time|. Clears daily limits.
@@ -191,6 +202,10 @@ class SiteEngagementService : public KeyedService,
   // upload.
   base::Time last_metrics_time_;
 
+  // A list of observers. When any origin registers an engagement-increasing
+  // event, each observer's OnEngagementIncreased method will be called.
+  base::ObserverList<SiteEngagementObserver> observer_list_;
+
   base::WeakPtrFactory<SiteEngagementService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SiteEngagementService);