TaskScheduler: Make method ordering consistent between...

TaskScheduler: Make method ordering consistent between SchedulerWorkerPoolImpl:: and SchedulerSingleThreadTaskRunnerManager::JoinForTesting

This is a follow-up to https://chromium-review.googlesource.com/c/chromium/src/+/1338140

Bug: 889029
Change-Id: I1c179f6617bac417fb54c55e9328e2391d2d7b5b
Reviewed-on: https://chromium-review.googlesource.com/c/1340360
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608942}

base/task/task_scheduler/scheduler_worker_pool_impl.cc

@@ -337,6 +337,8 @@ void SchedulerWorkerPoolImpl::JoinForTesting() {
   join_for_testing_started_.Set();
 #endif
 
+  shared_priority_queue_.EnableFlushSequencesOnDestroyForTesting();
+
   decltype(workers_) workers_copy;
   {
     AutoSchedulerLock auto_lock(lock_);
@@ -355,8 +357,6 @@ void SchedulerWorkerPoolImpl::JoinForTesting() {
   for (const auto& worker : workers_copy)
     worker->JoinForTesting();
 
-  shared_priority_queue_.EnableFlushSequencesOnDestroyForTesting();
-
   AutoSchedulerLock auto_lock(lock_);
   DCHECK(workers_ == workers_copy);
   // Release |workers_| to clear their TrackedRef against |this|.