Serializer: serialize internal references via object visitor.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index bfe162b752121d6fd1480f96f250ee5ef9f4fd2c..06d785eed0e9ee5a8131dfb7dbe11e9bd760f6e9 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -10943,9 +10943,12 @@ class ObjectVisitor BASE_EMBEDDED {
   // Visits an external reference embedded into a code object.
   virtual void VisitExternalReference(RelocInfo* rinfo);
 
-  // Visits an external reference. The value may be modified on return.
+  // Visits an external reference.
   virtual void VisitExternalReference(Address* p) {}
 
+  // Visits an (encoded) internal reference.
+  virtual void VisitInternalReference(RelocInfo* rinfo) {}
+
   // Visits a handle that has an embedder-assigned class ID.
   virtual void VisitEmbedderReference(Object** p, uint16_t class_id) {}