ntp_tiles: Add tests covering tile-fetching logic

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 b4c9660b05a828a2e3c833a747a8ab6c949b78b5..cb553f0502d78d0718357cfeaad234fbd03217bc 100644
--- a/components/ntp_tiles/most_visited_sites.h
+++ b/components/ntp_tiles/most_visited_sites.h
@@ -28,9 +28,8 @@ namespace history {
 class TopSites;
 }
 
-namespace user_prefs {
-class PrefRegistrySyncable;
-}
+class PrefRegistrySimple;
+class PrefService;
 
 class PrefService;
 
@@ -116,7 +115,7 @@ class MostVisitedSites : public history::TopSitesObserver,
   // MostVisitedSitesSupervisor::Observer implementation.
   void OnBlockedSitesChanged() override;
 
-  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+  static void RegisterProfilePrefs(PrefRegistrySimple* registry);
 
   // Workhorse for SaveNewTiles. Implemented as a separate static and public
   // method for ease of testing.