Both v8/src/compiler/operation-typer.cc and v8/src/compiler/typer.cc declare a:

Type* JSType(Type* type) {
  if (type->Is(Type::Boolean())) return Type::Boolean();
  if (type->Is(Type::String())) return Type::String();
  if (type->Is(Type::Number())) return Type::Number();
  if (type->Is(Type::Undefined())) return Type::Undefined();
  if (type->Is(Type::Null())) return Type::Null();
  if (type->Is(Type::Symbol())) return Type::Symbol();
  if (type->Is(Type::Receiver())) return Type::Receiver();  // JS "Object"
  return Type::Any();
}

If operation-typer.cc and typer.cc end up in the same jumbo unit (they don't see to do by default but they did in my local tests with jumbo_file_merge_limit=100) that will even cause a compilation failure.

I guess the best would be to find a shared place to put it, but I'm not familiar enough with the v8 src to know such a place by heart.