Added CHECKs for null pointers in ChromeAppSorting.

extensions/browser/null_app_sorting.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_NULL_APP_SORTING_H_
 #define EXTENSIONS_BROWSER_NULL_APP_SORTING_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "extensions/browser/app_sorting.h"
 
 namespace extensions {
 
 // An AppSorting that doesn't provide any ordering.
 class NullAppSorting : public AppSorting {
  public:
   NullAppSorting();
   ~NullAppSorting() override;
 
   // AppSorting overrides:
   void SetExtensionScopedPrefs(ExtensionScopedPrefs* prefs) override;
+  void CheckExtensionScopedPrefs() const override;
   void SetExtensionSyncService(
       ExtensionSyncService* extension_sync_service) override;
   void Initialize(const ExtensionIdList& extension_ids) override;
   void FixNTPOrdinalCollisions() override;
   void EnsureValidOrdinals(
       const std::string& extension_id,
       const syncer::StringOrdinal& suggested_page) override;
   void OnExtensionMoved(const std::string& moved_extension_id,
                         const std::string& predecessor_extension_id,
                         const std::string& successor_extension_id) override;
@@ skipping 19 matching lines @@
   void SetExtensionVisible(const std::string& extension_id,
                            bool visible) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NullAppSorting);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_NULL_APP_SORTING_H_