[LookupIterator] Add fast-path for reloading accessor property information

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 1cbff613def4d48aed00f521eb007863fbe8c18a..c6421b997d66f9bc6ac975ef25ea449165b63cbe 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -368,10 +368,18 @@ void LookupIterator::TransitionToAccessorProperty(
     Handle<Map> old_map(receiver->map(), isolate_);
     Handle<Map> new_map = Map::TransitionToAccessorProperty(
         old_map, name_, component, accessor, attributes);
+    bool simple_transition = new_map->GetBackPointer() == receiver->map();
     JSObject::MigrateToMap(receiver, new_map);
 
-    ReloadPropertyInformation();
+    if (simple_transition) {
+      int number = new_map->LastAdded();

[jochen (gone - plz use gerrit), 2016/03/04 09:58:03]

why's LastAdded not return uint32_t?

+      number_ = static_cast<uint32_t>(number);
+      property_details_ = new_map->GetLastDescriptorDetails();
+      state_ = ACCESSOR;
+      return;
+    }
 
+    ReloadPropertyInformation();
     if (!new_map->is_dictionary_map()) return;
   }