[turbofan] Properly implement %_ClassOf intrinsic.

src/compiler/js-intrinsic-lowering.h

Index: src/compiler/js-intrinsic-lowering.h
diff --git a/src/compiler/js-intrinsic-lowering.h b/src/compiler/js-intrinsic-lowering.h
index efbda1f710e75591c7687234775f108cafb6ceb3..50fcd8ce2b67df44864a6e9c4b08a3c0188933ce 100644
--- a/src/compiler/js-intrinsic-lowering.h
+++ b/src/compiler/js-intrinsic-lowering.h
@@ -67,6 +67,10 @@ class V8_EXPORT_PRIVATE JSIntrinsicLowering final
   Reduction ReduceStringGetRawHashField(Node* node);
   Reduction ReduceTheHole(Node* node);
 
+  // TODO(turbofan): JavaScript builtins support; drop once all uses of
+  // %_ClassOf in JavaScript builtins are eliminated.
+  Reduction ReduceClassOf(Node* node);
+
   Reduction Change(Node* node, const Operator* op);
   Reduction Change(Node* node, const Operator* op, Node* a, Node* b);
   Reduction Change(Node* node, const Operator* op, Node* a, Node* b, Node* c);