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

components/scheduler/renderer/idle_time_estimator.h

Index: components/scheduler/renderer/idle_time_estimator.h
diff --git a/components/scheduler/renderer/idle_time_estimator.h b/components/scheduler/renderer/idle_time_estimator.h
index eb9eee3d95e73c71f448c4df896115681e50385e..af00fbbeff35bd64c905d7bbf1799f0823101b68 100644
--- a/components/scheduler/renderer/idle_time_estimator.h
+++ b/components/scheduler/renderer/idle_time_estimator.h
@@ -18,6 +18,7 @@ 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);
 
@@ -36,12 +37,10 @@ class SCHEDULER_EXPORT IdleTimeEstimator
   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_;