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

base/task_scheduler/task.cc

Index: base/task_scheduler/task.cc
diff --git a/base/task_scheduler/task.cc b/base/task_scheduler/task.cc
index 5a17b7f2093ee2668a4de8b6bc85f681e27823f7..7314099c43a8a53a957a5c527690e5ae30155867 100644
--- a/base/task_scheduler/task.cc
+++ b/base/task_scheduler/task.cc
@@ -22,7 +22,8 @@ Task::Task(const tracked_objects::Location& posted_from,
                          TaskShutdownBehavior::BLOCK_SHUTDOWN
                  ? TaskTraits(traits).WithShutdownBehavior(
                        TaskShutdownBehavior::SKIP_ON_SHUTDOWN)
-                 : traits) {}
+                 : traits),
+      delay(delay) {}
 
 Task::~Task() = default;