Finalize backend for fetching more NTPSnippets.

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 7e5742e94fc6d4796c9f9b7c9249ff1c5f0918fb..f7230d78d5fe8762d4ec9482310cbc7687ee140a 100644
--- a/components/ntp_snippets/content_suggestions_provider.h
+++ b/components/ntp_snippets/content_suggestions_provider.h
@@ -5,6 +5,7 @@
 #ifndef COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
 
+#include <set>
 #include <string>
 #include <vector>
 
@@ -31,7 +32,7 @@ class ContentSuggestionsProvider {
   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)>;
 
   // The observer of a provider is notified when new data is available.
@@ -102,11 +103,13 @@ 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 been provided. The given |callback|
-  // is called with these suggestion, along with all existing suggestions.
-  virtual void FetchMore(const Category& category,
-                         FetchedMoreCallback callback) = 0;
+  // Fetches more suggestions for the given category. The new suggestions
+  // will not include any suggestion of the |known_suggestion_ids| sets.
+  // The given |callback| is called with these suggestions, along with all
+  // existing suggestions.
+  virtual void Fetch(const Category& category,
+                     std::set<std::string> known_suggestion_ids,
+                     FetchingCallback callback) = 0;
 
   // Removes history from the specified time range where the URL matches the
   // |filter|. The data removed depends on the provider. Note that the