FetchMore functionality backend

components/ntp_snippets/content_suggestions_provider.h

 // Copyright 2016 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_CONTENT_SUGGESTIONS_PROVIDER_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 82 matching lines @@
       const ContentSuggestion::ID& suggestion_id) = 0;
 
   // Fetches the image for the suggestion with the given ID and returns it
   // through the callback. This fetch may occur locally or from the internet.
   // If that suggestion doesn't exist, doesn't have an image or if the fetch
   // fails, the callback gets a null image. The callback will not be called
   // synchronously.
   virtual void FetchSuggestionImage(const ContentSuggestion::ID& suggestion_id,
                                     const ImageFetchedCallback& callback) = 0;
 
+  // A user-triggered request to fetch more content for the given category.
+  // Provides only suggestions that have not already been provided.

[Marc Treib, 2016/10/18 08:17:45]

There's no "given category" - there probably should be? One provider can provide
more than one category.
How does it provide suggestions? There's no return value or callback.

[fhorschig, 2016/10/20 13:10:38]

Done. It used to notificate an Observer. Now there is a callback.
The category was included. The backend doesn't support a category filter yet so
all categories are fetched and unwanted ones are discarded.

+  virtual void FetchMore() = 0;
+
   // Removes history from the specified time range where the URL matches the
   // |filter|. The data removed depends on the provider. Note that the
   // data outside the time range may be deleted, for example suggestions, which
   // are based on history from that time range. Providers should immediately
   // clear any data related to history from the specified time range where the
   // URL matches the |filter|.
   virtual void ClearHistory(
       base::Time begin,
       base::Time end,
       const base::Callback<bool(const GURL& url)>& filter) = 0;
@@ skipping 26 matching lines @@
   CategoryFactory* category_factory() const { return category_factory_; }
 
  private:
   Observer* observer_;
   CategoryFactory* category_factory_;
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_