ntp_tiles: Migrate to multi-observer model

components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc

Index: components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
diff --git a/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc b/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
index 4dce944c2442d3d0334c869d55c90f57fda900dc..c1948d71081e341621db779b2f35e3c831ee9c6c 100644
--- a/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
+++ b/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
@@ -24,7 +24,7 @@ NTPTilesInternalsMessageHandlerClient::
     ~NTPTilesInternalsMessageHandlerClient() = default;
 
 NTPTilesInternalsMessageHandler::NTPTilesInternalsMessageHandler()
-    : client_(nullptr), site_count_(8) {}
+    : client_(nullptr) {}
 
 NTPTilesInternalsMessageHandler::~NTPTilesInternalsMessageHandler() = default;
 
@@ -49,7 +49,8 @@ void NTPTilesInternalsMessageHandler::HandleRegisterForEvents(
   SendSourceInfo();
 
   most_visited_sites_ = client_->MakeMostVisitedSites();
-  most_visited_sites_->SetMostVisitedURLsObserver(this, site_count_);
+  most_visited_sites_->AddObserver(this);
+  most_visited_sites_->Refresh();
 }
 
 void NTPTilesInternalsMessageHandler::HandleUpdate(
@@ -92,7 +93,8 @@ void NTPTilesInternalsMessageHandler::HandleUpdate(
   // TODO(sfiera): refresh MostVisitedSites without re-creating it, as soon as
   // that will pick up changes to the Popular Sites overrides.
   most_visited_sites_ = client_->MakeMostVisitedSites();
-  most_visited_sites_->SetMostVisitedURLsObserver(this, site_count_);
+  most_visited_sites_->AddObserver(this);
+  most_visited_sites_->Refresh();
   SendSourceInfo();
 }