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

components/scheduler/renderer/task_cost_estimator.cc

 // 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.
 
 #include "components/scheduler/renderer/task_cost_estimator.h"
 
 #include "base/time/default_tick_clock.h"
 
 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) {}
 
 TaskCostEstimator::~TaskCostEstimator() {}
 
 void TaskCostEstimator::WillProcessTask(const base::PendingTask& pending_task) {
   // Avoid measuring the duration in nested run loops.
   if (++outstanding_task_count_ == 1)
     task_start_time_ = time_source_->NowTicks();
 }
 
 void TaskCostEstimator::DidProcessTask(const base::PendingTask& pending_task) {
   if (--outstanding_task_count_ == 0) {
     base::TimeDelta duration = time_source_->NowTicks() - task_start_time_;
     rolling_time_delta_history_.InsertSample(duration);
   }
 }
 
 base::TimeDelta TaskCostEstimator::expected_task_duration() const {
   return rolling_time_delta_history_.Percentile(estimation_percentile_);
 }
 
 void TaskCostEstimator::Clear() {
   rolling_time_delta_history_.Clear();
   expected_task_duration_ = base::TimeDelta();
 }
 
-void TaskCostEstimator::SetTimeSourceForTesting(
-    scoped_ptr<base::TickClock> time_source) {
-  time_source_ = time_source.Pass();
-}
-
 }  // namespace scheduler