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 TaskQueueManager::PumpQueue(size_t queue_index) {
  DCHECK(main_thread_checker_.CalledOnValidThread());
  internal::TaskQueue* queue = Queue(queue_index);
  queue->PumpQueue();
}

void TaskQueueManager::PumpQueue(size_t queue_index) {
  DCHECK(main_thread_checker_.CalledOnValidThread());
  internal::TaskQueue* queue = Queue(queue_index);
  queue->PumpQueue();
}
