[runtime] Object.create(null) creates a slow object

src/runtime/runtime-object.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/debug/debug.h"
 #include "src/isolate-inl.h"
@@ skipping 208 matching lines @@
   }
 
   // Generate the map with the specified {prototype} based on the Object
   // function's initial map from the current native context.
   // TODO(bmeurer): Use a dedicated cache for Object.create; think about
   // slack tracking for Object.create.
   Handle<Map> map(isolate->native_context()->object_function()->initial_map(),
                   isolate);
   if (map->prototype() != *prototype) {
     if (prototype->IsNull(isolate)) {
-      map = isolate->object_with_null_prototype_map();
+      map = isolate->slow_object_with_null_prototype_map();
     } else if (prototype->IsJSObject()) {
       Handle<JSObject> js_prototype = Handle<JSObject>::cast(prototype);
       if (!js_prototype->map()->is_prototype_map()) {
         JSObject::OptimizeAsPrototype(js_prototype, FAST_PROTOTYPE);
       }
       Handle<PrototypeInfo> info =
           Map::GetOrCreatePrototypeInfo(js_prototype, isolate);
       // TODO(verwaest): Use inobject slack tracking for this map.
       if (info->HasObjectCreateMap()) {
         map = handle(info->ObjectCreateMap(), isolate);
       } else {
         map = Map::CopyInitialMap(map);
         Map::SetPrototype(map, prototype, FAST_PROTOTYPE);
         PrototypeInfo::SetObjectCreateMap(info, map);
       }
     } else {
       map = Map::TransitionToPrototype(map, prototype, REGULAR_PROTOTYPE);
     }
   }
 
   // Actually allocate the object.
   Handle<JSObject> object = isolate->factory()->NewJSObjectFromMap(map);
 
+  if (map->is_dictionary_map()) {
+    Handle<NameDictionary> properties =
+        NameDictionary::New(isolate, NameDictionary::kInitialCapacity);
+    object->set_properties(*properties);
+  }
+
   // Define the properties if properties was specified and is not undefined.
   Handle<Object> properties = args.at<Object>(1);
   if (!properties->IsUndefined(isolate)) {
     RETURN_FAILURE_ON_EXCEPTION(
         isolate, JSReceiver::DefineProperties(isolate, object, properties));
   }
 
   return *object;
 }
 
@@ skipping 672 matching lines @@
   if (!success) return isolate->heap()->exception();
   MAYBE_RETURN(
       JSReceiver::CreateDataProperty(&it, value, Object::THROW_ON_ERROR),
       isolate->heap()->exception());
   return *value;
 }
 
 
 }  // namespace internal
 }  // namespace v8