Scheduler/child/TimeSource could be replaced with base/time/DefaultTickClock.

They both are totally same and TimeSource is removed.

BUG=494892
R=skyostil@chromium.org, mithro@mithis.com

Review URL: https://codereview.chromium.org/1163143002

Cr-Commit-Position: refs/heads/master@{#333035}
void SchedulerHelper::SetPumpPolicy(size_t queue_index,
                                    TaskQueueManager::PumpPolicy pump_policy) {
  CheckOnValidThread();
  return task_queue_manager_->SetPumpPolicy(queue_index, pump_policy);
}

void SchedulerHelper::SetPumpPolicy(size_t queue_index,
                                    TaskQueueManager::PumpPolicy pump_policy) {
  CheckOnValidThread();
  return task_queue_manager_->SetPumpPolicy(queue_index, pump_policy);
}
