FetchMore functionality backend

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 be34e7290c43a0f9f3db422e13111c16b0fee6c6..3c3e74f3cff025ab64ca44b3c0e479b439213206 100644
--- a/components/ntp_snippets/content_suggestions_service.h
+++ b/components/ntp_snippets/content_suggestions_service.h
@@ -44,6 +44,8 @@ class ContentSuggestionsService : public KeyedService,
   using ImageFetchedCallback = base::Callback<void(const gfx::Image&)>;
   using DismissedSuggestionsCallback = base::Callback<void(
       std::vector<ContentSuggestion> dismissed_suggestions)>;
+  using FetchedMoreCallback =
+      base::Callback<void(std::vector<ContentSuggestion> suggestions)>;
 
   class Observer {
    public:
@@ -135,6 +137,11 @@ class ContentSuggestionsService : public KeyedService,
   // Returns whether |category| is dismissed.
   bool IsCategoryDismissed(Category category) const;
 
+  // Fetches additional contents for the given |category|. If the fetch was
+  // completed, the given |callback| is called with the updated content.

[vitaliii, 2016/11/01 23:29:57]

s/completed/successful?

[fhorschig, 2016/11/02 05:05:27]

It's also called if the call was not successful (e.g. the service wasn't ready
yet).

+  // This includes new and old data.
+  void FetchMore(const Category& category, const FetchedMoreCallback& callback);
+
   // Observer accessors.
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);