Implement PostDelayedTaskAt for guaranteed timer ordering

components/scheduler/child/null_task_queue.h

+// Copyright 2015 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_SCHEDULER_NULL_CHILD_TASK_QUEUE_H_
+#define COMPONENTS_SCHEDULER_NULL_CHILD_TASK_QUEUE_H_
+
+#include "components/scheduler/child/task_queue.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace scheduler {
+
+class SCHEDULER_EXPORT NullTaskQueue : public TaskQueue {
+ public:
+  NullTaskQueue(scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  // TaskQueue implementation
+  bool RunsTasksOnCurrentThread() const override;
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const base::Closure& task,
+                       base::TimeDelta delay) override;
+  bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
+                                  const base::Closure& task,
+                                  base::TimeDelta delay) override;
+  bool PostDelayedTaskAt(const tracked_objects::Location& from_here,
+                         const base::Closure& task,
+                         base::TimeTicks desired_run_time) override;
+
+ protected:
+  ~NullTaskQueue() override;
+
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(NullTaskQueue);
+};
+
+}  // namespace scheduler
+
+#endif  // COMPONENTS_SCHEDULER_CHILD_NULL_TASK_QUEUE_H_