ntp_tiles: Avoid redundant calls to TopSites

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..17fc09401aca9ade54aec7a93b8994161642364b 100644
--- a/components/ntp_tiles/most_visited_sites.h
+++ b/components/ntp_tiles/most_visited_sites.h
@@ -193,8 +193,9 @@ class MostVisitedSites : public history::TopSitesObserver,
 
   NTPTilesVector current_tiles_;
 
-  // For callbacks may be run after destruction.
-  base::WeakPtrFactory<MostVisitedSites> weak_ptr_factory_;
+  // For callbacks may be run after destruction, used exclusively for TopSites
+  // (since it's used to detect whether there's a query in flight).
+  base::WeakPtrFactory<MostVisitedSites> top_sites_weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MostVisitedSites);
 };