Make thread dumping more tolerant of broken invariants during abort.

Change-Id: Ie1bc20debe72f2ea2bf4c1be50cd9877c823670a
diff --git a/runtime/barrier.h b/runtime/barrier.h
index 167e1d6..5ca88e8 100644
--- a/runtime/barrier.h
+++ b/runtime/barrier.h
@@ -50,7 +50,7 @@
   // Counter, when this reaches 0 all people blocked on the barrier are signalled.
   int count_ GUARDED_BY(lock_);
 
-  Mutex lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
+  Mutex lock_ ACQUIRED_AFTER(Locks::abort_lock_);
   ConditionVariable condition_ GUARDED_BY(lock_);
 };