Plumb the handle signals state out of Waiter::Wait().

mojo/edk/system/message_pipe_test_utils.cc

Index: mojo/edk/system/message_pipe_test_utils.cc
diff --git a/mojo/edk/system/message_pipe_test_utils.cc b/mojo/edk/system/message_pipe_test_utils.cc
index eb779669550940b28b47a25306d64237be265ec2..25c6dfe25e1ca0327a70418cd0821b26c2c8a4fc 100644
--- a/mojo/edk/system/message_pipe_test_utils.cc
+++ b/mojo/edk/system/message_pipe_test_utils.cc
@@ -36,7 +36,8 @@ MojoResult WaitIfNecessary(MessagePipe* mp,
                                                       : add_result;
   }
 
-  MojoResult wait_result = waiter.Wait(MOJO_DEADLINE_INDEFINITE, nullptr);
+  MojoResult wait_result =
+      waiter.Wait(MOJO_DEADLINE_INDEFINITE, nullptr, nullptr);
   mp->RemoveAwakable(0, &waiter, signals_state);
   return wait_result;
 }