[NTP Snippets] Refactor background scheduling for remote suggestions

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 <set>
 #include <string>
 #include <vector>
@@ skipping 86 matching lines @@
 
   // 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. It has to be invoked exactly once as the front-end
   // might wait for its completion.
   virtual void Fetch(const Category& category,
                      const std::set<std::string>& known_suggestion_ids,
                      const FetchDoneCallback& callback) = 0;
 
+  // Reloads suggestions from all categories. If the suggestions change, the
+  // observer must be notified via OnNewSuggestions();
+  // TODO(jkcal): make pure virtual (involves touching all providers) or remove
+  // by resolving the pull/push dichotomy.
+  virtual void ReloadSuggestions() {}
+
   // 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 28 matching lines @@
   ContentSuggestionsProvider(Observer* observer);
 
   Observer* observer() const { return observer_; }
  private:
   Observer* observer_;
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_