Fix unobservable constructor replacement on prototype maps

src/factory.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/factory.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
 #include "src/conversions.h"
@@ skipping 38 matching lines @@
   result->set_value(*value);
   return result;
 }
 
 
 Handle<PrototypeInfo> Factory::NewPrototypeInfo() {
   Handle<PrototypeInfo> result =
       Handle<PrototypeInfo>::cast(NewStruct(PROTOTYPE_INFO_TYPE));
   result->set_prototype_users(WeakFixedArray::Empty());
   result->set_validity_cell(Smi::FromInt(0));
+  result->set_constructor_name(Smi::FromInt(0));
   return result;
 }
 
 
 Handle<Oddball> Factory::NewOddball(Handle<Map> map,
                                     const char* to_string,
                                     Handle<Object> to_number,
                                     byte kind) {
   Handle<Oddball> oddball = New<Oddball>(map, OLD_SPACE);
   Oddball::Initialize(isolate(), oddball, to_string, to_number, kind);
@@ skipping 2403 matching lines @@
   return Handle<Object>::null();
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
 
 } }  // namespace v8::internal