Implement PostDelayedTaskAt for guaranteed timer ordering

components/scheduler/child/worker_scheduler_impl.cc

Index: components/scheduler/child/worker_scheduler_impl.cc
diff --git a/components/scheduler/child/worker_scheduler_impl.cc b/components/scheduler/child/worker_scheduler_impl.cc
index b5b9c83af8c21e8c3e04772c5cf711343e8a7c54..21774d5aa47bbd87c8742501e76b7946aa7e3997 100644
--- a/components/scheduler/child/worker_scheduler_impl.cc
+++ b/components/scheduler/child/worker_scheduler_impl.cc
@@ -40,8 +40,7 @@ void WorkerSchedulerImpl::Init() {
   idle_helper_.EnableLongIdlePeriod();
 }
 
-scoped_refptr<base::SingleThreadTaskRunner>
-WorkerSchedulerImpl::DefaultTaskRunner() {
+scoped_refptr<TaskQueue> WorkerSchedulerImpl::DefaultTaskRunner() {
   DCHECK(initialized_);
   return helper_.DefaultTaskRunner();
 }