ntp_tiles: Migrate to multi-observer model

ios/chrome/browser/ui/ntp/google_landing_controller.mm

Index: ios/chrome/browser/ui/ntp/google_landing_controller.mm
diff --git a/ios/chrome/browser/ui/ntp/google_landing_controller.mm b/ios/chrome/browser/ui/ntp/google_landing_controller.mm
index edec1eab443e8cca6876fc08e4ae54c5f2e64378..aa8dd450e2a2baba5890965ec236e57a8287c2d8 100644
--- a/ios/chrome/browser/ui/ntp/google_landing_controller.mm
+++ b/ios/chrome/browser/ui/ntp/google_landing_controller.mm
@@ -121,7 +121,9 @@ namespace google_landing {
 class MostVisitedSitesObserverBridge
     : public ntp_tiles::MostVisitedSites::Observer {
  public:
-  MostVisitedSitesObserverBridge(GoogleLandingController* owner);
+  MostVisitedSitesObserverBridge(
+      GoogleLandingController* owner,
+      ntp_tiles::MostVisitedSites* most_visited_sites);
   ~MostVisitedSitesObserverBridge() override;
 
   // MostVisitedSites::Observer implementation.
@@ -131,13 +133,19 @@ class MostVisitedSitesObserverBridge
 
  private:
   GoogleLandingController* _owner;
+  ntp_tiles::MostVisitedSites* _most_visited_sites;  // weak
 };
 
 MostVisitedSitesObserverBridge::MostVisitedSitesObserverBridge(
-    GoogleLandingController* owner)
-    : _owner(owner) {}
+    GoogleLandingController* owner,
+    ntp_tiles::MostVisitedSites* most_visited_sites)
+    : _owner(owner), _most_visited_sites(most_visited_sites) {
+  _most_visited_sites->AddObserver(this);
+}
 
-MostVisitedSitesObserverBridge::~MostVisitedSitesObserverBridge() {}
+MostVisitedSitesObserverBridge::~MostVisitedSitesObserverBridge() {
+  _most_visited_sites->RemoveObserver(this);
+}
 
 void MostVisitedSitesObserverBridge::OnMostVisitedURLsAvailable(
     const ntp_tiles::NTPTilesVector& tiles) {
@@ -266,13 +274,13 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   // What's new promo.
   std::unique_ptr<NotificationPromoWhatsNew> _notification_promo;
 
+  std::unique_ptr<ntp_tiles::MostVisitedSites> _most_visited_sites;
+
   // A MostVisitedSites::Observer bridge object to get notified of most visited
   // sites changes.
   std::unique_ptr<google_landing::MostVisitedSitesObserverBridge>
       _most_visited_observer_bridge;
 
-  std::unique_ptr<ntp_tiles::MostVisitedSites> _most_visited_sites;
-
   // URL of the last deleted most viewed entry. If present the UI to restore it
   // is shown.
   base::scoped_nsobject<NSURL> _deletedUrl;
@@ -931,9 +939,9 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   _most_visited_sites =
       IOSMostVisitedSitesFactory::NewForBrowserState(_browserState);
   _most_visited_observer_bridge.reset(
-      new google_landing::MostVisitedSitesObserverBridge(self));
-  _most_visited_sites->SetMostVisitedURLsObserver(
-      _most_visited_observer_bridge.get(), kMaxNumMostVisitedFavicons);
+      new google_landing::MostVisitedSitesObserverBridge(
+          self, _most_visited_sites.get()));
+  _most_visited_sites->Refresh();
 }
 
 - (void)updateSearchField {
@@ -1099,12 +1107,15 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
 
 - (void)onMostVisitedURLsAvailable:(const ntp_tiles::NTPTilesVector&)data {
   _mostVisitedData = data;
+  if (_mostVisitedData.size() > kMaxNumMostVisitedFavicons)

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

We're resizing to save memory, but it's not related to the number of tiles we're
actually going to show, is it? I think it would be good to have a comment in
this function explaining that we might show fewer than _mostVisitedData.size()
tiles, and a TODO to correct the impressions metrics accordingly (ios will make
you create a bug for a TODO; P3/sfiera is OK).

+    _mostVisitedData.resize(kMaxNumMostVisitedFavicons);
+
   [self reloadData];
 
-  if (data.size() && !_recordedPageImpression) {
+  if (_mostVisitedData.size() && !_recordedPageImpression) {
     _recordedPageImpression = YES;
     std::vector<ntp_tiles::metrics::TileImpression> tiles;
-    for (const ntp_tiles::NTPTile& ntpTile : data) {
+    for (const ntp_tiles::NTPTile& ntpTile : _mostVisitedData) {
       tiles.emplace_back(ntpTile.source, ntp_tiles::metrics::UNKNOWN_TILE_TYPE,
                          ntpTile.url);
     }