[optimizing] Name the last DCE pass.

This will allow Checker to differentiate between them.

Change-Id: I972d452a64f1c19d370567b9ef3d620f9b835a9a
diff --git a/compiler/optimizing/constant_folding_test.cc b/compiler/optimizing/constant_folding_test.cc
index e420a62..02ad675 100644
--- a/compiler/optimizing/constant_folding_test.cc
+++ b/compiler/optimizing/constant_folding_test.cc
@@ -62,7 +62,7 @@
 
   check_after_cf(graph);
 
-  HDeadCodeElimination(graph, nullptr).Run();
+  HDeadCodeElimination(graph).Run();
   SSAChecker ssa_checker_dce(&allocator, graph);
   ssa_checker_dce.Run();
   ASSERT_TRUE(ssa_checker_dce.IsValid());