Fixes an invalidated pointer access in NTPSnipppetsFetcher.

components/ntp_snippets/remote/ntp_snippets_service.h

 // Copyright 2015 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_SNIPPETS_REMOTE_NTP_SNIPPETS_SERVICE_H_
 #define COMPONENTS_NTP_SNIPPETS_REMOTE_NTP_SNIPPETS_SERVICE_H_
 
 #include <cstddef>
 #include <map>
 #include <memory>
@@ skipping 101 matching lines @@
   void RescheduleFetching(bool force);
 
   // ContentSuggestionsProvider implementation
   CategoryStatus GetCategoryStatus(Category category) override;
   CategoryInfo GetCategoryInfo(Category category) override;
   void DismissSuggestion(const ContentSuggestion::ID& suggestion_id) override;
   void FetchSuggestionImage(const ContentSuggestion::ID& suggestion_id,
                             const ImageFetchedCallback& callback) override;
   void Fetch(const Category& category,
              const std::set<std::string>& known_suggestion_ids,
-             FetchingCallback callback) override;
+             const FetchingCallback& callback) override;
   void ClearHistory(
       base::Time begin,
       base::Time end,
       const base::Callback<bool(const GURL& url)>& filter) override;
   void ClearCachedSuggestions(Category category) override;
   void GetDismissedSuggestionsForDebugging(
       Category category,
       const DismissedSuggestionsCallback& callback) override;
   void ClearDismissedSuggestionsForDebugging(Category category) override;
 
@@ skipping 210 matching lines @@
 
     // Returns a non-dismissed snippet with the given |id_within_category|, or
     // null if none exist.
     const NTPSnippet* FindSnippet(const std::string& id_within_category) const;
 
     CategoryContent();
     CategoryContent(CategoryContent&&);
     ~CategoryContent();
     CategoryContent& operator=(CategoryContent&&);
   };
-  using CategoryContentMap =
-      std::map<Category, CategoryContent, Category::CompareByID>;
-  CategoryContentMap categories_;
+
+  std::map<Category, CategoryContent, Category::CompareByID> categories_;
 
   // The ISO 639-1 code of the language used by the application.
   const std::string application_language_code_;
 
   // Classifier that tells us how active the user is. Not owned.
   const UserClassifier* user_classifier_;
 
   // Scheduler for fetching snippets. Not owned.
   NTPSnippetsScheduler* scheduler_;
 
@@ skipping 21 matching lines @@
 
   // Request throttler for limiting requests to thumbnail images.
   RequestThrottler thumbnail_requests_throttler_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsService);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_REMOTE_NTP_SNIPPETS_SERVICE_H_