Finalize backend for fetching more NTPSnippets.

components/ntp_snippets/content_suggestions_service.h

Index: components/ntp_snippets/content_suggestions_service.h
diff --git a/components/ntp_snippets/content_suggestions_service.h b/components/ntp_snippets/content_suggestions_service.h
index 9b1b6664d6da5bd907a6ca7e6a037e8d47bc3dde..9cb37b200c8ea57ba26fbe162529b0a5e7472ec6 100644
--- a/components/ntp_snippets/content_suggestions_service.h
+++ b/components/ntp_snippets/content_suggestions_service.h
@@ -45,7 +45,7 @@ class ContentSuggestionsService : public KeyedService,
   using ImageFetchedCallback = base::Callback<void(const gfx::Image&)>;
   using DismissedSuggestionsCallback = base::Callback<void(
       std::vector<ContentSuggestion> dismissed_suggestions)>;
-  using FetchedMoreCallback =
+  using FetchingCallback =
       base::Callback<void(std::vector<ContentSuggestion> suggestions)>;
 
   class Observer {
@@ -141,7 +141,9 @@ class ContentSuggestionsService : public KeyedService,
   // Fetches additional contents for the given |category|. If the fetch was
   // completed, the given |callback| is called with the updated content.
   // This includes new and old data.
-  void FetchMore(const Category& category, const FetchedMoreCallback& callback);
+  void Fetch(const Category& category,
+             std::set<std::string> known_suggestion_ids,
+             const FetchingCallback& callback);
 
   // Observer accessors.
   void AddObserver(Observer* observer);