[turbofan] Build s/NULL/nullptr/g and CHECK(x != nullptr) to CHECK_NOT_NULL(x).

src/compiler/js-typed-lowering.cc

Index: src/compiler/js-typed-lowering.cc
diff --git a/src/compiler/js-typed-lowering.cc b/src/compiler/js-typed-lowering.cc
index 02cf180a0cb57a352338448bfe6c87769fa733df..a31aa0070c678217d1e4051170d21c7e88f5e217 100644
--- a/src/compiler/js-typed-lowering.cc
+++ b/src/compiler/js-typed-lowering.cc
@@ -1271,7 +1271,7 @@ Reduction JSTypedLowering::ReduceJSInstanceOf(Node* node) {
       jsgraph()->FalseConstant(), control);
 
   if (if_is_smi != nullptr) {
-    DCHECK(e_is_smi != nullptr);
+    DCHECK_NOT_NULL(e_is_smi);
     control = graph()->NewNode(common()->Merge(2), if_is_smi, control);
     effect =
         graph()->NewNode(common()->EffectPhi(2), e_is_smi, effect, control);