[NTP Snippets] Schedule periodic fetching

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 c3050298158d546902d795b01153755fae8d5850..29526e3cad4ff453b77d897b3ffad415b9662755 100644
--- a/components/ntp_snippets/ntp_snippets_service.h
+++ b/components/ntp_snippets/ntp_snippets_service.h
@@ -18,6 +18,7 @@
 #include "components/ntp_snippets/inner_iterator.h"
 #include "components/ntp_snippets/ntp_snippet.h"
 #include "components/ntp_snippets/ntp_snippets_fetcher.h"
+#include "components/ntp_snippets/ntp_snippets_scheduler.h"
 
 namespace ntp_snippets {
 
@@ -36,9 +37,12 @@ class NTPSnippetsService : public KeyedService, NTPSnippetsFetcher::Observer {
   // (British english person in the US) are not language code.
   NTPSnippetsService(scoped_refptr<base::SequencedTaskRunner> file_task_runner,
                      const std::string& application_language_code,
+                     NTPSnippetsScheduler* scheduler,
                      scoped_ptr<NTPSnippetsFetcher> snippets_fetcher);
   ~NTPSnippetsService() override;
 
+  void Init(bool enabled);
+
   // Fetches snippets from the server. |overwrite| is true if existing snippets
   // should be overwritten.
   void FetchSnippets(bool overwrite);
@@ -99,6 +103,9 @@ class NTPSnippetsService : public KeyedService, NTPSnippetsFetcher::Observer {
   // The observers.
   base::ObserverList<NTPSnippetsServiceObserver> observers_;
 
+  // Scheduler for fetching snippets. Not owned.
+  NTPSnippetsScheduler* scheduler_;
+
   // The snippets fetcher
   scoped_ptr<NTPSnippetsFetcher> snippets_fetcher_;