Adds a flag to support "Virtual Time" to the blink scheduler

components/scheduler/base/nestable_single_thread_task_runner.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_BASE_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_
-#define COMPONENTS_SCHEDULER_BASE_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_
-
-#include "base/single_thread_task_runner.h"
-#include "base/message_loop/message_loop.h"
-#include "components/scheduler/scheduler_export.h"
-
-namespace scheduler {
-
-// A single thread task runner which exposes whether it is running nested.
-class SCHEDULER_EXPORT NestableSingleThreadTaskRunner
-    : public base::SingleThreadTaskRunner {
- public:
-  NestableSingleThreadTaskRunner() {}
-
-  // Returns true if the task runner is nested (i.e., running a run loop within
-  // a nested task).
-  virtual bool IsNested() const = 0;
-
- protected:
-  ~NestableSingleThreadTaskRunner() override {}
-
-  DISALLOW_COPY_AND_ASSIGN(NestableSingleThreadTaskRunner);
-};
-
-}  // namespace scheduler
-
-#endif  // COMPONENTS_SCHEDULER_BASE_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_