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 39b424cdfc1402ed3c23624b8afd7c7e36c42cd4..eccf15c42ba4f8cdb9c00759d59aa8d0c4bd12e3 100644
--- a/base/threading/sequenced_worker_pool_unittest.cc
+++ b/base/threading/sequenced_worker_pool_unittest.cc
@@ -297,8 +297,7 @@ 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);
     }
   }