Separate the create and start phases in SchedulerWorkerPoolImpl.

base/task_scheduler/task_scheduler_impl.cc

Index: base/task_scheduler/task_scheduler_impl.cc
diff --git a/base/task_scheduler/task_scheduler_impl.cc b/base/task_scheduler/task_scheduler_impl.cc
index 3c98fdf4fd17f9791dd97f725cddfb6b1f3c14b1..9d0320caf1a247026bc22f7753c78f67f56f55bc 100644
--- a/base/task_scheduler/task_scheduler_impl.cc
+++ b/base/task_scheduler/task_scheduler_impl.cc
@@ -252,10 +252,11 @@ void TaskSchedulerImpl::Initialize(
     // Passing pointers to objects owned by |this| to
     // SchedulerWorkerPoolImpl::Create() is safe because a TaskSchedulerImpl
     // can't be deleted before all its worker pools have been joined.
-    worker_pools_.push_back(SchedulerWorkerPoolImpl::Create(
-        worker_pool_params, re_enqueue_sequence_callback, task_tracker_.get(),
+    worker_pools_.push_back(MakeUnique<SchedulerWorkerPoolImpl>(
+        worker_pool_params.name(), worker_pool_params.priority_hint(),
+        re_enqueue_sequence_callback, task_tracker_.get(),
         delayed_task_manager_.get()));
-    CHECK(worker_pools_.back());
+    worker_pools_.back()->Start(worker_pool_params);
   }
 }