[NTP Snippets] Don't reschedule background fetching on every startup

components/ntp_snippets/ntp_snippets_service.h

 // Copyright 2015 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_NTP_SNIPPETS_SERVICE_H_
 #define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SERVICE_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 90 matching lines @@
   // suggestions from the suggestion service) and adds them to the current ones.
   // Only called from chrome://snippets-internals, DO NOT USE otherwise!
   // Ignored while ready() is false.
   void FetchSnippetsFromHosts(const std::set<std::string>& hosts,
                               bool interactive_request);
 
   const NTPSnippetsFetcher* snippets_fetcher() const {
     return snippets_fetcher_.get();
   }
 
-  // (Re)schedules the periodic fetching of snippets.
-  void RescheduleFetching();
+  // (Re)schedules the periodic fetching of snippets. If |force| is true, the
+  // tasks will be re-scheduled even if they already exist and have the correct
+  // periods.
+  void RescheduleFetching(bool force);
 
   // ContentSuggestionsProvider implementation
   CategoryStatus GetCategoryStatus(Category category) override;
   CategoryInfo GetCategoryInfo(Category category) override;
   void DismissSuggestion(const std::string& suggestion_id) override;
   void FetchSuggestionImage(const std::string& suggestion_id,
                             const ImageFetchedCallback& callback) override;
   void ClearHistory(
       base::Time begin,
       base::Time end,
@@ skipping 236 matching lines @@
 
   // Request throttler for limiting requests to thumbnail images.
   RequestThrottler thumbnail_requests_throttler_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsService);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SERVICE_H_