Generator objects have [[Class]] === "Generator"

src/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4343 matching lines @@
 MaybeObject* Heap::AllocateJSGeneratorObject(JSFunction *function) {
   ASSERT(function->shared()->is_generator());
   Map *map;
   if (function->has_initial_map()) {
     map = function->initial_map();
   } else {
     // Allocate the initial map if absent.
     MaybeObject* maybe_map = AllocateInitialMap(function);
     if (!maybe_map->To(&map)) return maybe_map;
     function->set_initial_map(map);
+    map->set_constructor(function);
   }
   ASSERT(map->instance_type() == JS_GENERATOR_OBJECT_TYPE);
   return AllocateJSObjectFromMap(map);
 }
 
 
 MaybeObject* Heap::AllocateJSModule(Context* context, ScopeInfo* scope_info) {
   // Allocate a fresh map. Modules do not have a prototype.
   Map* map;
   MaybeObject* maybe_map = AllocateMap(JS_MODULE_TYPE, JSModule::kSize);
@@ skipping 3486 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   FIXED_ARRAY_SUB_INSTANCE_TYPE_LIST(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   memcpy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   memcpy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal