FetchMore functionality backend

components/ntp_snippets/remote/ntp_snippets_fetcher.h

Index: components/ntp_snippets/remote/ntp_snippets_fetcher.h
diff --git a/components/ntp_snippets/remote/ntp_snippets_fetcher.h b/components/ntp_snippets/remote/ntp_snippets_fetcher.h
index ce40c5539207362b11a8693ce4f235ef76aad2c8..382021f575dd5400895e922280ec47ec5a3d513c 100644
--- a/components/ntp_snippets/remote/ntp_snippets_fetcher.h
+++ b/components/ntp_snippets/remote/ntp_snippets_fetcher.h
@@ -65,7 +65,7 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
   // occur, |snippets| contains no value (no actual vector in base::Optional).
   // Error details can be retrieved using last_status().
   using SnippetsAvailableCallback =
-      base::Callback<void(OptionalFetchedCategories fetched_categories)>;
+      base::OnceCallback<void(OptionalFetchedCategories fetched_categories)>;
 
   // Enumeration listing all possible outcomes for fetch attempts. Used for UMA
   // histograms, so do not change existing values. Insert new values at the end,
@@ -112,6 +112,9 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
     // user action. Typically, non-interactive requests are subject to a daily
     // quota.
     bool interactive_request = false;
+
+    // If set, only return results for this category.
+    base::Optional<Category> exclusive_category;
   };
 
   NTPSnippetsFetcher(
@@ -126,17 +129,13 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
       const UserClassifier* user_classifier);
   ~NTPSnippetsFetcher() override;
 
-  // Set a callback that is called when a new set of snippets are downloaded,
-  // overriding any previously set callback.
-  void SetCallback(const SnippetsAvailableCallback& callback);
-
   // Initiates a fetch from the server. When done (successfully or not), calls
   // the subscriber of SetCallback().
   //
   // If an ongoing fetch exists, it will be silently abandoned and a new one
   // started, without triggering an additional callback (i.e. the callback will
   // only be called once).
-  void FetchSnippets(const Params& params);
+  void FetchSnippets(const Params& params, SnippetsAvailableCallback callback);
 
   // Debug string representing the status/result of the last fetch attempt.
   const std::string& last_status() const { return last_status_; }
@@ -227,6 +226,7 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
   void FetchFinished(OptionalFetchedCategories fetched_categories,
                      FetchResult result,
                      const std::string& extra_message);
+  void FilterCategories(FetchedCategoriesVector* categories);
 
   bool DemandQuotaForRequest(bool interactive_request);