[runtime] Add fast path to update LookupIterator in simple cases

src/lookup.h

Index: src/lookup.h
diff --git a/src/lookup.h b/src/lookup.h
index 48048bb51dc33a9721a9328a143345cb84a1638b..60f171c2d79d7c565c6f2380a060d37e1e92ad89 100644
--- a/src/lookup.h
+++ b/src/lookup.h
@@ -287,11 +287,13 @@ class LookupIterator final BASE_EMBEDDED {
     return (configuration_ & kInterceptor) != 0;
   }
   int descriptor_number() const {
+    DCHECK(!IsElement());
     DCHECK(has_property_);
     DCHECK(!holder_map_->is_dictionary_map());
     return number_;
   }
   int dictionary_entry() const {
+    DCHECK(!IsElement());
     DCHECK(has_property_);
     DCHECK(holder_map_->is_dictionary_map());
     return number_;