ntp_tiles: Migrate to multi-observer model

chrome/browser/search/instant_service.cc

Index: chrome/browser/search/instant_service.cc
diff --git a/chrome/browser/search/instant_service.cc b/chrome/browser/search/instant_service.cc
index 3d5863dbb45a41b4987ce9f464745cb2a868e13c..abfbe96f1716054e95c55627f56cb2fe188d6261 100644
--- a/chrome/browser/search/instant_service.cc
+++ b/chrome/browser/search/instant_service.cc
@@ -103,7 +103,7 @@ InstantService::InstantService(Profile* profile)
   if (base::FeatureList::IsEnabled(kNtpTilesFeature)) {
     most_visited_sites_ =
         ChromeMostVisitedSitesFactory::NewForProfile(profile_);
-    most_visited_sites_->SetMostVisitedURLsObserver(this, 8);
+    most_visited_sites_->AddObserver(this);

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

Here, you're not doing any filtering to produce 8 tiles. I assume that means we
can provide >8 tiles to JS now. Have you tested this with the bing or yandex
NTPs?

   } else {
     top_sites_ = TopSitesFactory::GetForProfile(profile_);
     if (top_sites_) {
@@ -151,6 +151,8 @@ InstantService::InstantService(Profile* profile)
 }
 
 InstantService::~InstantService() {
+  if (most_visited_sites_)
+    most_visited_sites_->RemoveObserver(this);
   if (template_url_service_)
     template_url_service_->RemoveObserver(this);
 }