[turbofan] Ensure that NTLs are always properly connected to the end.

test/unittests/compiler/graph-unittest.cc

Index: test/unittests/compiler/graph-unittest.cc
diff --git a/test/unittests/compiler/graph-unittest.cc b/test/unittests/compiler/graph-unittest.cc
index 8c77ef14d14c4da32308e0d96c4ed130929227b6..956c86745f69dea562a29ddeb642c334fbf37219 100644
--- a/test/unittests/compiler/graph-unittest.cc
+++ b/test/unittests/compiler/graph-unittest.cc
@@ -13,6 +13,7 @@ namespace compiler {
 
 GraphTest::GraphTest(int num_parameters) : common_(zone()), graph_(zone()) {
   graph()->SetStart(graph()->NewNode(common()->Start(num_parameters)));
+  graph()->SetEnd(graph()->NewNode(common()->End(), graph()->start()));
 }
 
 
@@ -92,6 +93,12 @@ Matcher<Node*> GraphTest::IsTrueConstant() {
 }
 
 
+Matcher<Node*> GraphTest::IsUndefinedConstant() {
+  return IsHeapConstant(
+      Unique<HeapObject>::CreateImmovable(factory()->undefined_value()));
+}
+
+
 TypedGraphTest::TypedGraphTest(int num_parameters)
     : GraphTest(num_parameters),
       typer_(isolate(), graph(), MaybeHandle<Context>()) {}