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

components/scheduler/renderer/task_cost_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_TASK_COST_ESTIMATOR_H_
 #define COMPONENTS_SCHEDULER_RENDERER_TASK_COST_ESTIMATOR_H_
 
 #include "base/message_loop/message_loop.h"
 #include "base/time/time.h"
 #include "cc/base/rolling_time_delta_history.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace base {
 class TickClock;
 }
 
 namespace scheduler {
 
 // Estimates the cost of running tasks based on historical timing data.
 class SCHEDULER_EXPORT TaskCostEstimator
     : public base::MessageLoop::TaskObserver {
  public:
-  TaskCostEstimator(int sample_count, double estimation_percentile);
+  TaskCostEstimator(base::TickClock* time_source,
+                    int sample_count,
+                    double estimation_percentile);
   ~TaskCostEstimator() override;
 
   base::TimeDelta expected_task_duration() const;
 
   // TaskObserver implementation:
   void WillProcessTask(const base::PendingTask& pending_task) override;
   void DidProcessTask(const base::PendingTask& pending_task) override;
 
   void Clear();
 
-  void SetTimeSourceForTesting(scoped_ptr<base::TickClock> time_source);
-
  private:
   cc::RollingTimeDeltaHistory rolling_time_delta_history_;
-  scoped_ptr<base::TickClock> time_source_;
+  base::TickClock* time_source_;  // NOT OWNED
   int outstanding_task_count_;
   double estimation_percentile_;
   base::TimeTicks task_start_time_;
   base::TimeDelta expected_task_duration_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskCostEstimator);
 };
 
 }  // namespace scheduler
 
 #endif  // COMPONENTS_SCHEDULER_RENDERER_TASK_COST_ESTIMATOR_H_