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

components/scheduler/renderer/idle_time_estimator.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_RENDERER_IDLE_TIME_ESTIMATOR_H_
 #define COMPONENTS_SCHEDULER_RENDERER_IDLE_TIME_ESTIMATOR_H_
 
 #include "base/message_loop/message_loop.h"
 #include "base/time/tick_clock.h"
 #include "cc/base/rolling_time_delta_history.h"
 #include "components/scheduler/base/task_queue.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace scheduler {
 
 // Estimates how much idle time there is available.  Ignores nested tasks.
 class SCHEDULER_EXPORT IdleTimeEstimator
     : public base::MessageLoop::TaskObserver {
  public:
   IdleTimeEstimator(const scoped_refptr<TaskQueue>& compositor_task_runner,
+                    base::TickClock* time_source,
                     int sample_count,
                     double estimation_percentile);
 
   ~IdleTimeEstimator() override;
 
   // Expected Idle time is defined as: |compositor_frame_interval| minus
   // expected compositor task duration.
   base::TimeDelta GetExpectedIdleDuration(
       base::TimeDelta compositor_frame_interval) const;
 
   void DidCommitFrameToCompositor();
 
   void Clear();
 
   // TaskObserver implementation:
   void WillProcessTask(const base::PendingTask& pending_task) override;
   void DidProcessTask(const base::PendingTask& pending_task) override;
 
-  void SetTimeSourceForTesting(scoped_ptr<base::TickClock> time_source);
-
  private:
   scoped_refptr<TaskQueue> compositor_task_runner_;
   cc::RollingTimeDeltaHistory per_frame_compositor_task_runtime_;
-  scoped_ptr<base::TickClock> time_source_;
+  base::TickClock* time_source_;  // NOT OWNED
   double estimation_percentile_;
 
   base::TimeTicks task_start_time_;
   base::TimeTicks prev_commit_time_;
   base::TimeDelta cumulative_compositor_runtime_;
   int nesting_level_;
   bool did_commit_;
 
   DISALLOW_COPY_AND_ASSIGN(IdleTimeEstimator);
 };
 
 }  // namespace scheduler
 
 #endif  // COMPONENTS_SCHEDULER_RENDERER_IDLE_TIME_ESTIMATOR_H_