Enable TaskSchedulerTaskTrackerTest SingletonAllowed Tests on POSIX

base/task_scheduler/task_tracker_unittest.cc

Index: base/task_scheduler/task_tracker_unittest.cc
diff --git a/base/task_scheduler/task_tracker_unittest.cc b/base/task_scheduler/task_tracker_unittest.cc
index bbfff4285687b59c2f46f38d138de707395c284f..fedb215669889f409018bfa0b2577cc4051ffb3e 100644
--- a/base/task_scheduler/task_tracker_unittest.cc
+++ b/base/task_scheduler/task_tracker_unittest.cc
@@ -382,13 +382,11 @@ TEST_P(TaskSchedulerTaskTrackerTest, SingletonAllowed) {
     tracker.RunNextTaskInSequence(
         CreateSequenceWithTask(std::move(task)).get());
   } else {
-#if !defined(OS_LINUX)  // http://crbug.com/634552
     EXPECT_DCHECK_DEATH(
         {
           tracker.RunNextTaskInSequence(
               CreateSequenceWithTask(std::move(task)).get());
         });
-#endif  // !defined(OS_LINUX)
   }
 }