[NTP Snippets] Schedule periodic fetching

components/ntp_snippets/ntp_snippets_scheduler.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_NTP_SNIPPETS_SCHEDULER_H_
+#define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SCHEDULER_H_
+
+#include "base/macros.h"
+
+namespace ntp_snippets {
+
+// Interface to schedule the periodic fetching of snippets.
+class NTPSnippetsScheduler {
+ public:
+  // Schedule periodic fetching of snippets every |period_seconds|. The
+  // concrete implementation should call NTPSnippetsService::FetchSnippets once
+  // per period.
+  virtual bool Schedule(int period_seconds) = 0;
+
+  // Cancel the scheduled fetching task, if any.
+  virtual bool Unschedule() = 0;
+
+ protected:
+  NTPSnippetsScheduler() = default;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NTPSnippetsScheduler);
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SCHEDULER_H_