ntp_tiles: Migrate to multi-observer model

components/ntp_tiles/most_visited_sites.h

Index: components/ntp_tiles/most_visited_sites.h
diff --git a/components/ntp_tiles/most_visited_sites.h b/components/ntp_tiles/most_visited_sites.h
index 17fc09401aca9ade54aec7a93b8994161642364b..ef3f1d5d1298af9d19352d2add92fd6a017bca92 100644
--- a/components/ntp_tiles/most_visited_sites.h
+++ b/components/ntp_tiles/most_visited_sites.h
@@ -14,6 +14,7 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
 #include "base/scoped_observer.h"
 #include "base/strings/string16.h"
 #include "components/history/core/browser/history_types.h"
@@ -77,7 +78,7 @@ class MostVisitedSitesSupervisor {
 class MostVisitedSites : public history::TopSitesObserver,
                          public MostVisitedSitesSupervisor::Observer {
  public:
-  // The observer to be notified when the list of most visited sites changes.
+  // Observer to be notified when the list of most visited sites changes.
   class Observer {
    public:
     virtual void OnMostVisitedURLsAvailable(const NTPTilesVector& tiles) = 0;
@@ -92,6 +93,8 @@ class MostVisitedSites : public history::TopSitesObserver,
   // |prefs| and |suggestions| are required and may not be null. |top_sites|,
   // |popular_sites|, and |supervisor| are optional and if null the associated
   // features will be disabled.
+  //
+  // Clients must call Refresh() to fetch the initial tiles.
   MostVisitedSites(PrefService* prefs,
                    scoped_refptr<history::TopSites> top_sites,
                    suggestions::SuggestionsService* suggestions,
@@ -101,15 +104,15 @@ class MostVisitedSites : public history::TopSitesObserver,
 
   ~MostVisitedSites() override;
 
-  // Sets the observer, and immediately fetches the current suggestions.
-  // Does not take ownership of |observer|, which must outlive this object and
-  // must not be null.
-  void SetMostVisitedURLsObserver(Observer* observer, int num_sites);
+  // Observer registration.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
 
-  // Requests an asynchronous refresh of the suggestions. Notifies the observer
+  // Requests an asynchronous refresh of the suggestions. Notifies the observers
   // once the request completes.

[sfiera, 2017/01/18 09:58:33]

This is now also necessary after every AddObserver() call, right? (there is no
way to get the current state, only updates)

   void Refresh();
 
+  // Blacklist manipulation.
   void AddOrRemoveBlacklistedUrl(const GURL& url, bool add_url);
   void ClearBlacklistedUrls();
 
@@ -156,9 +159,9 @@ class MostVisitedSites : public history::TopSitesObserver,
   // if appropriate, and saves the new tiles.
   void SaveNewTiles(NTPTilesVector personal_tiles);
 
-  // Notifies the observer about the availability of tiles.
+  // Notifies the observers about the availability of tiles.
   // Also records impressions UMA if not done already.
-  void NotifyMostVisitedURLsObserver();
+  void NotifyMostVisitedURLsObservers();
 
   void OnPopularSitesAvailable(bool success);
 
@@ -176,10 +179,7 @@ class MostVisitedSites : public history::TopSitesObserver,
   std::unique_ptr<IconCacher> const icon_cacher_;
   std::unique_ptr<MostVisitedSitesSupervisor> supervisor_;
 
-  Observer* observer_;
-
-  // The maximum number of most visited sites to return.
-  int num_sites_;
+  base::ObserverList<Observer> observer_list_;
 
   std::unique_ptr<
       suggestions::SuggestionsService::ResponseCallbackList::Subscription>