Finalize backend for fetching more NTPSnippets.

components/ntp_snippets/remote/ntp_snippets_service.h

Index: components/ntp_snippets/remote/ntp_snippets_service.h
diff --git a/components/ntp_snippets/remote/ntp_snippets_service.h b/components/ntp_snippets/remote/ntp_snippets_service.h
index a330622b8af979adec4f0490734ba8cad514933e..0bf8891b197badd990b1454745851751a40f50fc 100644
--- a/components/ntp_snippets/remote/ntp_snippets_service.h
+++ b/components/ntp_snippets/remote/ntp_snippets_service.h
@@ -117,8 +117,9 @@ class NTPSnippetsService final : public ContentSuggestionsProvider,
   void DismissSuggestion(const ContentSuggestion::ID& suggestion_id) override;
   void FetchSuggestionImage(const ContentSuggestion::ID& suggestion_id,
                             const ImageFetchedCallback& callback) override;
-  void FetchMore(const Category& category,
-                 FetchedMoreCallback callback) override;
+  void Fetch(const Category& category,
+             std::set<std::string> known_suggestion_ids,
+             FetchingCallback callback) override;
   void ClearHistory(
       base::Time begin,
       base::Time end,
@@ -213,7 +214,7 @@ class NTPSnippetsService final : public ContentSuggestionsProvider,
   // Callback for the NTPSnippetsFetcher.
   void OnFetchFinished(
       bool fetched_more,
-      FetchedMoreCallback fetched_more_callback,
+      FetchingCallback fetched_more_callback,
       NTPSnippetsFetcher::OptionalFetchedCategories fetched_categories);
 
   // Moves all snippets from |to_archive| into the archive of the |category|.
@@ -285,7 +286,7 @@ class NTPSnippetsService final : public ContentSuggestionsProvider,
 
   // Converts the cached snippets in the given |category| to content suggestions
   // and passes them to the |callback|.
-  void NotifyMoreSuggestions(Category category, FetchedMoreCallback callback);
+  void NotifyMoreSuggestions(Category category, FetchingCallback callback);
 
   // Updates the internal status for |category| to |category_status_| and
   // notifies the content suggestions observer if it changed.
@@ -296,19 +297,22 @@ class NTPSnippetsService final : public ContentSuggestionsProvider,
   void RestoreCategoriesFromPrefs();
   void StoreCategoriesToPrefs();
 
-  // Implementation for |FetchSnippets| and |FetchMore| that calls the snippet
+  // Implementation for |FetchSnippets| and |Fetch| that calls the snippet
   // fetcher and replaces or adds the fetched snippets depending on the
   // |fetch_more| parameter.
   void FetchSnippetsFromHostsImpl(const std::set<std::string>& hosts,
                                   bool interactive_request,
                                   bool fetch_more,
-                                  FetchedMoreCallback fetched_more_callback,
-                                  base::Optional<Category> exclusive_category);
+                                  std::set<std::string> known_suggestion_ids,
+                                  base::Optional<Category> exclusive_category,
+                                  FetchingCallback fetched_more_callback);
 
-  // Returns a set of snippet IDs that should not be fetcheds. These IDs always
+  // Returns a set of snippet IDs that should not be fetched. These IDs always
   // include dismissed snippets. If |fetch_more| is set, they include all known
   // snippet IDs.
-  std::set<std::string> CollectIdsToExclude(bool fetch_more) const;
+  std::set<std::string> CollectIdsToExclude(
+      bool fetch_more,
+      std::set<std::string> additional_ids) const;
 
   void MarkEmptyCategoriesAsLoading();