Use constexpr TaskTraits constructor in base (part 2).

base/observer_list_unittest.cc

Index: base/observer_list_unittest.cc
diff --git a/base/observer_list_unittest.cc b/base/observer_list_unittest.cc
index d0248c90faf1bf39847690b67d04fd9635393bb2..d2c3493179b1af0344ac9e0f0534dae1df9ade15 100644
--- a/base/observer_list_unittest.cc
+++ b/base/observer_list_unittest.cc
@@ -600,7 +600,7 @@ TEST(ObserverListThreadSafeTest, RemoveWhileNotificationIsRunning) {
   // TaskScheduler can safely use |barrier|.
   test::ScopedTaskEnvironment scoped_task_environment;
 
-  CreateSequencedTaskRunnerWithTraits(TaskTraits().WithBaseSyncPrimitives())
+  CreateSequencedTaskRunnerWithTraits({WithBaseSyncPrimitives()})
       ->PostTask(FROM_HERE,
                  base::Bind(&ObserverListThreadSafe<Foo>::AddObserver,
                             observer_list, Unretained(&observer)));