FetchMore functionality backend

components/ntp_snippets/content_suggestions_provider.h

Index: components/ntp_snippets/content_suggestions_provider.h
diff --git a/components/ntp_snippets/content_suggestions_provider.h b/components/ntp_snippets/content_suggestions_provider.h
index f6741356d66e6cfc0a3773c83c8afe25a6d63d83..82b8e5b569fe1112069eca1d3d70e244b24805b6 100644
--- a/components/ntp_snippets/content_suggestions_provider.h
+++ b/components/ntp_snippets/content_suggestions_provider.h
@@ -100,6 +100,10 @@ class ContentSuggestionsProvider {
   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