Synchronize memory in TaskTracker::Flush().

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index a8fbfcac856d1ccca41dc61a0921841d52102b7f..a209a25e4ad8cc9ece50db6aa46a385309398d7c 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -215,7 +215,7 @@ void TaskTracker::Shutdown() {
 
 void TaskTracker::Flush() {
   AutoSchedulerLock auto_lock(flush_lock_);
-  while (subtle::NoBarrier_Load(&num_pending_undelayed_tasks_) != 0 &&
+  while (subtle::Acquire_Load(&num_pending_undelayed_tasks_) != 0 &&
          !IsShutdownComplete()) {
     flush_cv_->Wait();
   }
@@ -484,7 +484,7 @@ void TaskTracker::OnBlockingShutdownTasksComplete() {
 
 void TaskTracker::DecrementNumPendingUndelayedTasks() {
   const auto new_num_pending_undelayed_tasks =
-      subtle::NoBarrier_AtomicIncrement(&num_pending_undelayed_tasks_, -1);
+      subtle::Barrier_AtomicIncrement(&num_pending_undelayed_tasks_, -1);
   DCHECK_GE(new_num_pending_undelayed_tasks, 0);
   if (new_num_pending_undelayed_tasks == 0) {
     AutoSchedulerLock auto_lock(flush_lock_);