TaskScheduler: Replace the SchedulerServiceThread with a base::Thread.

base/task_scheduler/scheduler_worker_pool.h

Index: base/task_scheduler/scheduler_worker_pool.h
diff --git a/base/task_scheduler/scheduler_worker_pool.h b/base/task_scheduler/scheduler_worker_pool.h
index 43dce606c6285fa68fc5797eeaf715bea3b52e69..db0e6c35b9fa5e107a6c98524db511545a279917 100644
--- a/base/task_scheduler/scheduler_worker_pool.h
+++ b/base/task_scheduler/scheduler_worker_pool.h
@@ -43,11 +43,11 @@ class BASE_EXPORT SchedulerWorkerPool {
   // |sequence|. If |worker| is non-null, |task| will be scheduled to run on it
   // specifically (note: |worker| must be owned by this SchedulerWorkerPool);
   // otherwise, |task| will be added to the pending shared work. |task| won't be
-  // executed before its delayed run time, if any. Returns true if |task| is
-  // posted.
+  // executed before its |delay| expires. Returns true if |task| is posted.
   virtual bool PostTaskWithSequence(std::unique_ptr<Task> task,
                                     scoped_refptr<Sequence> sequence,
-                                    SchedulerWorker* worker) = 0;
+                                    SchedulerWorker* worker,
+                                    TimeDelta delay) = 0;
 
   // Posts |task| to be executed by this SchedulerWorkerPool as part of
   // |sequence|. If |worker| is non-null, |task| will be scheduled to run on it