Fix ntp-tiles-internals crash in incognito mode

components/ntp_tiles/webui/ntp_tiles_internals_message_handler_client.h

 // Copyright 2016 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_WEBUI_NTP_TILES_INTERNALS_MESSAGE_HANDLER_CLIENT_H_
 #define COMPONENTS_NTP_TILES_WEBUI_NTP_TILES_INTERNALS_MESSAGE_HANDLER_CLIENT_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 13 matching lines @@
 
 class MostVisitedSites;
 class PopularSites;
 
 // Implemented by embedders to hook up NTPTilesInternalsMessageHandler.
 class NTPTilesInternalsMessageHandlerClient {
  public:
   // Returns the PrefService for the embedder and containing WebUI page.
   virtual PrefService* GetPrefs() = 0;
 
+  // False if in a browser mode (e.g. incognito) where tiles aren't supported.
+  virtual bool SupportsNTPTiles() = 0;
+
   // Returns true if the given source is enabled (even if, in practice, none of
   // the tiles would come from it).
   virtual bool DoesSourceExist(NTPTileSource source) = 0;
 
   // Creates a new MostVisitedSites based on the context pf the WebUI page.
   virtual std::unique_ptr<ntp_tiles::MostVisitedSites>
   MakeMostVisitedSites() = 0;
 
   // Creates a new PopularSites based on the context pf the WebUI page.
   virtual std::unique_ptr<ntp_tiles::PopularSites> MakePopularSites() = 0;
@@ skipping 18 matching lines @@
   NTPTilesInternalsMessageHandlerClient();
   virtual ~NTPTilesInternalsMessageHandlerClient();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NTPTilesInternalsMessageHandlerClient);
 };
 
 }  // namespace ntp_tiles
 
 #endif  // COMPONENTS_NTP_TILES_WEBUI_NTP_TILES_INTERNALS_MESSAGE_HANDLER_CLIENT_H_