Add a simple scheduler for animation frames

mc/scheduler/timer.h

+// Copyright 2014 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 MC_SCHEDULER_TIMER_H_
+#define MC_SCHEDULER_TIMER_H_
+
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/time.h"
+#include "mc/scheduler/time_interval.h"
+
+namespace mc {
+
+class Timer {
+ public:
+  class Client {
+   public:
+    virtual void OnTimerTick(base::TimeTicks now) = 0;
+
+   protected:
+    virtual ~Client();
+  };
+
+  Timer(Client* client,
+        scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~Timer();
+
+  void SetInterval(const TimeInterval& parameters);
+  void SetEnabled(bool enabled);
+
+ private:
+  base::TimeTicks NextTickTarget(base::TimeTicks now);
+  void ScheduleNextTick(base::TimeTicks now);
+  void PostTickTask(base::TimeTicks now, base::TimeTicks target);
+  void OnTimerFired();
+
+  Client* client_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  TimeInterval interval_;
+  base::TimeTicks last_tick_;
+  base::TimeTicks current_target_;
+
+  bool enabled_;
+
+  base::WeakPtrFactory<Timer> weak_factory_;
+};
+}
+
+#endif  // MC_SCHEDULER_TIMER_H_