[optimizing] Name the last DCE pass.

This will allow Checker to differentiate between them.

Change-Id: I972d452a64f1c19d370567b9ef3d620f9b835a9a
diff --git a/compiler/optimizing/dead_code_elimination_test.cc b/compiler/optimizing/dead_code_elimination_test.cc
index 6350019..98ae1ec 100644
--- a/compiler/optimizing/dead_code_elimination_test.cc
+++ b/compiler/optimizing/dead_code_elimination_test.cc
@@ -44,7 +44,7 @@
   std::unique_ptr<const X86InstructionSetFeatures> features_x86(
       X86InstructionSetFeatures::FromCppDefines());
   x86::CodeGeneratorX86 codegenX86(graph, *features_x86.get(), CompilerOptions());
-  HDeadCodeElimination(graph, nullptr).Run();
+  HDeadCodeElimination(graph).Run();
   SSAChecker ssa_checker(&allocator, graph);
   ssa_checker.Run();
   ASSERT_TRUE(ssa_checker.IsValid());