Implement an observer interface for the site engagement service.

chrome/browser/engagement/site_engagement_service.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 #define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 
 #include <map>
 #include <memory>
 #include <set>
 
 #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"
 
 namespace base {
 class DictionaryValue;
 class Clock;
 }
 
 namespace history {
@@ skipping 75 matching lines @@
 
   // Update the last time |url| was opened from an installed shortcut to be
   // clock_->Now().
   void SetLastShortcutLaunchTime(const GURL& url);
 
   // Overridden from SiteEngagementScoreProvider.
   double GetScore(const GURL& url) const override;
   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);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, GetMedianEngagement);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, GetTotalNavigationPoints);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, GetTotalUserInputPoints);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, LastShortcutLaunch);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest,
                            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);
 
   // Only used in tests.
   SiteEngagementService(Profile* profile, std::unique_ptr<base::Clock> clock);
 
   // Adds the specified number of points to the given origin, respecting the
   // maximum limits for the day and overall.
   void AddPoints(const GURL& url, double points);
 
   // Post startup tasks: cleaning up origins which have decayed to 0, and
   // logging UMA statistics.
   void AfterStartupTask();
   void CleanupEngagementScores();
   void RecordMetrics();
 
   // 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;

[benwells, 2016/06/01 01:44:45]

This doesn't appear to be used or tested. Are you planning to use it? If not I
don't think its worth adding for completeness sake alone.

[dominickn, 2016/06/01 02:54:13]

Acknowledged, I'll remove it.

+
   // 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.
   void HandleMediaPlaying(const GURL& url, bool is_hidden);
 
   // Update the engagement score of the origin matching |url| for navigation.
   void HandleNavigation(const GURL& url, ui::PageTransition transition);
 
   // Update the engagement score of the origin matching |url| for time-on-site,
   // based on user input.
@@ skipping 13 matching lines @@
   int OriginsWithMaxEngagement(const std::map<GURL, double>& score_map) const;
 
   // Callback for the history service when it is asked for a map of origins to
   // how many URLs corresponding to that origin remain in history.
   void GetCountsAndLastVisitForOriginsComplete(
     history::HistoryService* history_service,
     const std::multiset<GURL>& deleted_url_origins,
     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.
   void ResetScoreAndAccessTimesForURL(const GURL& url,
                                       double score,
                                       const base::Time* updated_time);
 
   Profile* profile_;
 
   // The clock used to vend times.
   std::unique_ptr<base::Clock> clock_;
 
   // Metrics are recorded at non-incognito browser startup, and then
   // approximately once per hour thereafter. Store the local time at which
   // metrics were previously uploaded: the first event which affects any
   // origin's engagement score after an hour has elapsed triggers the next
   // 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);
 };
 
 #endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_