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

components/scheduler/renderer/task_cost_estimator.cc

Index: components/scheduler/renderer/task_cost_estimator.cc
diff --git a/components/scheduler/renderer/task_cost_estimator.cc b/components/scheduler/renderer/task_cost_estimator.cc
index 910760dff42ab6a764499ff2e4e430667bbbb81d..ce8dee9087546b7054025c9a5129cc11eb47bbca 100644
--- a/components/scheduler/renderer/task_cost_estimator.cc
+++ b/components/scheduler/renderer/task_cost_estimator.cc
@@ -8,10 +8,11 @@
 
 namespace scheduler {
 
-TaskCostEstimator::TaskCostEstimator(int sample_count,
+TaskCostEstimator::TaskCostEstimator(base::TickClock* time_source,
+                                     int sample_count,
                                      double estimation_percentile)
     : rolling_time_delta_history_(sample_count),
-      time_source_(new base::DefaultTickClock),
+      time_source_(time_source),
       outstanding_task_count_(0),
       estimation_percentile_(estimation_percentile) {}
 
@@ -39,9 +40,4 @@ void TaskCostEstimator::Clear() {
   expected_task_duration_ = base::TimeDelta();
 }
 
-void TaskCostEstimator::SetTimeSourceForTesting(
-    scoped_ptr<base::TickClock> time_source) {
-  time_source_ = time_source.Pass();
-}
-
 }  // namespace scheduler