Allow top_sites to be null.

components/ntp_tiles/most_visited_sites.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_NTP_TILES_MOST_VISITED_SITES_H_
 #define COMPONENTS_NTP_TILES_MOST_VISITED_SITES_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 95 matching lines @@
    public:
     virtual void OnMostVisitedURLsAvailable(const NTPTilesVector& tiles) = 0;
     virtual void OnPopularURLsAvailable(const PopularSitesVector& sites) {}
 
    protected:
     virtual ~Observer() {}
   };
 
   // Construct a MostVisitedSites instance.
   //
-  // |prefs|, |top_sites|, and |suggestions| are required and may not be null.
-  // |popular_sites| and |supervisor| are optional and if null the associated
+  // |prefs| and |suggestions| are required and may not be null. |top_sites|,
+  // |popular_sites|, and |supervisor| are optional and if null the associated
   // features will be disabled.
   MostVisitedSites(PrefService* prefs,
                    scoped_refptr<history::TopSites> top_sites,
                    suggestions::SuggestionsService* suggestions,
                    std::unique_ptr<PopularSites> popular_sites,
                    MostVisitedSitesSupervisor* supervisor);
 
   ~MostVisitedSites() override;
 
   // Does not take ownership of |observer|, which must outlive this object and
@@ skipping 103 matching lines @@
 
   // For callbacks may be run after destruction.
   base::WeakPtrFactory<MostVisitedSites> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MostVisitedSites);
 };
 
 }  // namespace ntp_tiles
 
 #endif  // COMPONENTS_NTP_TILES_MOST_VISITED_SITES_H_