ntp_tiles: Migrate to multi-observer model

components/ntp_tiles/most_visited_sites.cc

Index: components/ntp_tiles/most_visited_sites.cc
diff --git a/components/ntp_tiles/most_visited_sites.cc b/components/ntp_tiles/most_visited_sites.cc
index 6f5504cf5792fe285357ef8244b746727b91b821..8ddd45ba66f579990548554fc52dbd6df2475961 100644
--- a/components/ntp_tiles/most_visited_sites.cc
+++ b/components/ntp_tiles/most_visited_sites.cc
@@ -30,6 +30,8 @@ namespace ntp_tiles {
 
 namespace {
 
+constexpr int kNumTilesForObservers = 12;
+
 const base::Feature kDisplaySuggestionsServiceTiles{
     "DisplaySuggestionsServiceTiles", base::FEATURE_ENABLED_BY_DEFAULT};
 
@@ -59,8 +61,6 @@ MostVisitedSites::MostVisitedSites(
       popular_sites_(std::move(popular_sites)),
       icon_cacher_(std::move(icon_cacher)),
       supervisor_(std::move(supervisor)),
-      observer_(nullptr),
-      num_sites_(0),
       top_sites_observer_(this),
       mv_source_(NTPTileSource::TOP_SITES),
       top_sites_weak_ptr_factory_(this) {
@@ -70,22 +70,10 @@ MostVisitedSites::MostVisitedSites(
   DCHECK(suggestions_service_);
   if (supervisor_)
     supervisor_->SetObserver(this);
-}
-
-MostVisitedSites::~MostVisitedSites() {
-  if (supervisor_)
-    supervisor_->SetObserver(nullptr);
-}
-
-void MostVisitedSites::SetMostVisitedURLsObserver(Observer* observer,
-                                                  int num_sites) {
-  DCHECK(observer);
-  observer_ = observer;
-  num_sites_ = num_sites;
 
   // The order for this condition is important, ShouldShowPopularSites() should
   // always be called last to keep metrics as relevant as possible.
-  if (popular_sites_ && NeedPopularSites(prefs_, num_sites_) &&
+  if (popular_sites_ && NeedPopularSites(prefs_, kNumTilesForObservers) &&
       ShouldShowPopularSites()) {
     popular_sites_->StartFetch(
         false, base::Bind(&MostVisitedSites::OnPopularSitesAvailable,
@@ -93,10 +81,6 @@ void MostVisitedSites::SetMostVisitedURLsObserver(Observer* observer,
   }
 
   if (top_sites_) {
-    // TopSites updates itself after a delay. To ensure up-to-date results,
-    // force an update now.
-    top_sites_->SyncWithHistory();
-
     // Register as TopSitesObserver so that we can update ourselves when the
     // TopSites changes.
     top_sites_observer_.Add(top_sites_.get());
@@ -105,15 +89,33 @@ void MostVisitedSites::SetMostVisitedURLsObserver(Observer* observer,
   suggestions_subscription_ = suggestions_service_->AddCallback(
       base::Bind(&MostVisitedSites::OnSuggestionsProfileAvailable,
                  base::Unretained(this)));
+}
+
+MostVisitedSites::~MostVisitedSites() {
+  if (supervisor_)
+    supervisor_->SetObserver(nullptr);
+}
+
+void MostVisitedSites::AddObserver(Observer* observer) {
+  observer_list_.AddObserver(observer);
+}
+
+void MostVisitedSites::RemoveObserver(Observer* observer) {
+  observer_list_.RemoveObserver(observer);
+}
+
+void MostVisitedSites::Refresh() {
+  // TODO(mastiz): Refresh PopularSites too if enabled.
+
+  // TopSites updates itself after a delay. To ensure up-to-date results, force
+  // an update now.
+  if (top_sites_)
+    top_sites_->SyncWithHistory();
 
   // Immediately build the current set of tiles, getting suggestions from the
   // SuggestionsService's cache or, if that is empty, sites from TopSites.
   BuildCurrentTiles();
   // Also start a request for fresh suggestions.
-  Refresh();
-}
-
-void MostVisitedSites::Refresh() {
   suggestions_service_->FetchSuggestionsData();
 }
 
@@ -197,7 +199,7 @@ void MostVisitedSites::OnMostVisitedURLsAvailable(
 
   NTPTilesVector tiles;
   size_t num_tiles =
-      std::min(visited_list.size(), static_cast<size_t>(num_sites_));
+      std::min(visited_list.size(), static_cast<size_t>(kNumTilesForObservers));
   for (size_t i = 0; i < num_tiles; ++i) {
     const history::MostVisitedURL& visited = visited_list[i];
     if (visited.url.is_empty()) {
@@ -218,7 +220,7 @@ void MostVisitedSites::OnMostVisitedURLsAvailable(
 
   mv_source_ = NTPTileSource::TOP_SITES;
   SaveNewTiles(std::move(tiles));
-  NotifyMostVisitedURLsObserver();
+  NotifyMostVisitedURLsObservers();
 }
 
 void MostVisitedSites::OnSuggestionsProfileAvailable(
@@ -231,8 +233,8 @@ void MostVisitedSites::OnSuggestionsProfileAvailable(
     InitiateTopSitesQuery();
     return;
   }
-  if (num_sites_ < num_tiles)
-    num_tiles = num_sites_;
+  if (kNumTilesForObservers < num_tiles)
+    num_tiles = kNumTilesForObservers;
 
   NTPTilesVector tiles;
   for (int i = 0; i < num_tiles; ++i) {
@@ -254,7 +256,7 @@ void MostVisitedSites::OnSuggestionsProfileAvailable(
 
   mv_source_ = NTPTileSource::SUGGESTIONS_SERVICE;
   SaveNewTiles(std::move(tiles));
-  NotifyMostVisitedURLsObserver();
+  NotifyMostVisitedURLsObservers();
 }
 
 NTPTilesVector MostVisitedSites::CreateWhitelistEntryPointTiles(
@@ -264,9 +266,9 @@ NTPTilesVector MostVisitedSites::CreateWhitelistEntryPointTiles(
   }
 
   size_t num_personal_tiles = personal_tiles.size();
-  DCHECK_LE(num_personal_tiles, static_cast<size_t>(num_sites_));
+  DCHECK_LE(num_personal_tiles, static_cast<size_t>(kNumTilesForObservers));
 
-  size_t num_whitelist_tiles = num_sites_ - num_personal_tiles;
+  size_t num_whitelist_tiles = kNumTilesForObservers - num_personal_tiles;
   NTPTilesVector whitelist_tiles;
 
   std::set<std::string> personal_hosts;
@@ -309,11 +311,11 @@ NTPTilesVector MostVisitedSites::CreatePopularSitesTiles(
     return NTPTilesVector();
 
   size_t num_tiles = personal_tiles.size() + whitelist_tiles.size();
-  DCHECK_LE(num_tiles, static_cast<size_t>(num_sites_));
+  DCHECK_LE(num_tiles, static_cast<size_t>(kNumTilesForObservers));
 
   // Collect non-blacklisted popular suggestions, skipping those already present
   // in the personal suggestions.
-  size_t num_popular_sites_tiles = num_sites_ - num_tiles;
+  size_t num_popular_sites_tiles = kNumTilesForObservers - num_tiles;
   NTPTilesVector popular_sites_tiles;
 
   if (num_popular_sites_tiles > 0 && popular_sites_) {
@@ -355,7 +357,7 @@ void MostVisitedSites::SaveNewTiles(NTPTilesVector personal_tiles) {
 
   size_t num_actual_tiles = personal_tiles.size() + whitelist_tiles.size() +
                             popular_sites_tiles.size();
-  DCHECK_LE(num_actual_tiles, static_cast<size_t>(num_sites_));
+  DCHECK_LE(num_actual_tiles, static_cast<size_t>(kNumTilesForObservers));
 
   current_tiles_ =
       MergeTiles(std::move(personal_tiles), std::move(whitelist_tiles),
@@ -384,11 +386,9 @@ NTPTilesVector MostVisitedSites::MergeTiles(NTPTilesVector personal_tiles,
   return merged_tiles;
 }
 
-void MostVisitedSites::NotifyMostVisitedURLsObserver() {
-  if (!observer_)
-    return;
-
-  observer_->OnMostVisitedURLsAvailable(current_tiles_);
+void MostVisitedSites::NotifyMostVisitedURLsObservers() {
+  for (Observer& observer : observer_list_)
+    observer.OnMostVisitedURLsAvailable(current_tiles_);
 }
 
 void MostVisitedSites::OnPopularSitesAvailable(bool success) {
@@ -403,8 +403,8 @@ void MostVisitedSites::OnPopularSitesAvailable(bool success) {
 
 void MostVisitedSites::OnIconMadeAvailable(const GURL& site_url,
                                            bool newly_available) {
-  if (newly_available)
-    observer_->OnIconMadeAvailable(site_url);
+  for (Observer& observer : observer_list_)
+    observer.OnIconMadeAvailable(site_url);
 }
 
 void MostVisitedSites::TopSitesLoaded(TopSites* top_sites) {}