Prepare GetProperty(Attributes)WithInterceptor to support elements

src/lookup.h

Index: src/lookup.h
diff --git a/src/lookup.h b/src/lookup.h
index 849ce57bd668bd2dbad7b1581907e0f1915c9a29..b8e7c4d2b3b3640572fecdb0cc04fa9e810bfde4 100644
--- a/src/lookup.h
+++ b/src/lookup.h
@@ -126,7 +126,17 @@ class LookupIterator final BASE_EMBEDDED {
   Isolate* isolate() const { return isolate_; }
   State state() const { return state_; }
 
-  Handle<Name> name() const { return name_; }
+  Handle<Name> name() const {
+    DCHECK(!IsElement());
+    return name_;
+  }
+  Handle<Name> GetName() {
+    if (name_.is_null()) {
+      DCHECK(IsElement());
+      name_ = isolate_->factory()->Uint32ToString(index_);
+    }
+    return name_;
+  }
   uint32_t index() const { return index_; }
 
   bool IsElement() const { return index_ != kMaxUInt32; }