Create base::test::ScopedTaskScheduler.

base/threading/sequenced_worker_pool_unittest.cc

Index: base/threading/sequenced_worker_pool_unittest.cc
diff --git a/base/threading/sequenced_worker_pool_unittest.cc b/base/threading/sequenced_worker_pool_unittest.cc
index 5782af7e767b631bffcb0c3551895ea9a55a2d02..f4f9e600111e7a3308167e30235b20e29305a740 100644
--- a/base/threading/sequenced_worker_pool_unittest.cc
+++ b/base/threading/sequenced_worker_pool_unittest.cc
@@ -287,8 +287,7 @@ class SequencedWorkerPoolTest
   // Destroys and unregisters the registered TaskScheduler, if any.
   void DeleteTaskScheduler() {
     if (TaskScheduler::GetInstance()) {
-      static_cast<internal::TaskSchedulerImpl*>(TaskScheduler::GetInstance())
-          ->JoinForTesting();
+      TaskScheduler::GetInstance()->JoinForTesting();
       TaskScheduler::SetInstance(nullptr);
     }
   }