[NTP Snippets] Refactor background scheduling for remote suggestions

components/ntp_snippets/remote/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_REMOTE_NTP_SNIPPETS_SCHEDULER_H_
-#define COMPONENTS_NTP_SNIPPETS_REMOTE_NTP_SNIPPETS_SCHEDULER_H_
-
-#include "base/macros.h"
-#include "base/time/time.h"
-
-namespace ntp_snippets {
-
-// Interface to schedule the periodic fetching of snippets.
-class NTPSnippetsScheduler {
- public:
-  // Schedule periodic fetching of snippets, with different periods depending on
-  // network state. The concrete implementation should call
-  // NTPSnippetsService::FetchSnippets once per period.
-  // Any of the periods can be zero to indicate that the corresponding task
-  // should not be scheduled.
-  virtual bool Schedule(base::TimeDelta period_wifi,
-                        base::TimeDelta period_fallback) = 0;
-
-  // Cancel any scheduled tasks.
-  virtual bool Unschedule() = 0;
-
- protected:
-  NTPSnippetsScheduler() = default;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(NTPSnippetsScheduler);
-};
-
-}  // namespace ntp_snippets
-
-#endif  // COMPONENTS_NTP_SNIPPETS_REMOTE_NTP_SNIPPETS_SCHEDULER_H_