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 TaskQueue::TraceQueueSize(bool is_locked) const {
  bool is_tracing;
  TRACE_EVENT_CATEGORY_GROUP_ENABLED(disabled_by_default_tracing_category_,
                                     &is_tracing);
  if (!is_tracing || !name_)
    return;
  if (!is_locked)
    lock_.Acquire();
  else
    lock_.AssertAcquired();
  TRACE_COUNTER1(
      disabled_by_default_tracing_category_, name_,
      incoming_queue_.size() + work_queue_.size() + delayed_task_queue_.size());
  if (!is_locked)
    lock_.Release();
}

void TaskQueue::TraceQueueSize(bool is_locked) const {
  bool is_tracing;
  TRACE_EVENT_CATEGORY_GROUP_ENABLED(disabled_by_default_tracing_category_,
                                     &is_tracing);
  if (!is_tracing || !name_)
    return;
  if (!is_locked)
    lock_.Acquire();
  else
    lock_.AssertAcquired();
  TRACE_COUNTER1(
      disabled_by_default_tracing_category_, name_,
      incoming_queue_.size() + work_queue_.size() + delayed_task_queue_.size());
  if (!is_locked)
    lock_.Release();
}
