Fix broken tests

Change-Id: I9d0f1064e8cd63045283445946c46594a50d4b84
diff --git a/compiler/optimizing/graph_checker_test.cc b/compiler/optimizing/graph_checker_test.cc
index 659141f..2b82319 100644
--- a/compiler/optimizing/graph_checker_test.cc
+++ b/compiler/optimizing/graph_checker_test.cc
@@ -38,6 +38,7 @@
   graph->AddBlock(exit_block);
   graph->SetExitBlock(exit_block);
   entry_block->AddSuccessor(exit_block);
+  graph->BuildDominatorTree();
   return graph;
 }