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

components/ntp_snippets/ntp_snippets_service.h

Index: components/ntp_snippets/ntp_snippets_service.h
diff --git a/components/ntp_snippets/ntp_snippets_service.h b/components/ntp_snippets/ntp_snippets_service.h
index 3f4e5ff81eec4311db933a2c11b2f5f6ac5dff24..13a694c34b66d799656e045ed0d9cf9ef73ac3be 100644
--- a/components/ntp_snippets/ntp_snippets_service.h
+++ b/components/ntp_snippets/ntp_snippets_service.h
@@ -108,8 +108,10 @@ class NTPSnippetsService : public ContentSuggestionsProvider,
     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;