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 02501c73bb20668c20932c123e6239a90cc7d947..df9e63ebefb0b779ceb92fa9e5923dc4ecc7545a 100644
--- a/src/lookup.h
+++ b/src/lookup.h
@@ -120,7 +120,17 @@ 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<String> GetName() {
+    if (name_.is_null()) {
+      DCHECK(IsElement());
+      name_ = isolate_->factory()->Uint32ToString(index_);
+    }
+    return Handle<String>::cast(name_);
+  }
   uint32_t index() const { return index_; }
 
   bool IsElement() const { return index_ != kMaxUInt32; }