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::SetWorkBatchSizeForTesting(size_t work_batch_size) {
  CheckOnValidThread();
  task_queue_manager_->SetWorkBatchSize(work_batch_size);
}

void SchedulerHelper::SetWorkBatchSizeForTesting(size_t work_batch_size) {
  CheckOnValidThread();
  task_queue_manager_->SetWorkBatchSize(work_batch_size);
}
