Make setting of accessors even more atomic.

src/api.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 3046 matching lines @@
                          v8::Handle<Value> data,
                          AccessControl settings,
                          PropertyAttribute attributes) {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   ON_BAILOUT(isolate, "v8::Object::SetAccessor()", return false);
   ENTER_V8(isolate);
   i::HandleScope scope(isolate);
   i::Handle<i::AccessorInfo> info = MakeAccessorInfo(name,
                                                      getter, setter, data,
                                                      settings, attributes);
+  bool fast = Utils::OpenHandle(this)->HasFastProperties();
   i::Handle<i::Object> result = i::SetAccessor(Utils::OpenHandle(this), info);
-  return !result.is_null() && !result->IsUndefined();
+  if (result.is_null() || result->IsUndefined()) return false;
+  if (fast) i::JSObject::TransformToFastProperties(Utils::OpenHandle(this), 0);
+  return true;
 }
 
 
 bool v8::Object::HasOwnProperty(Handle<String> key) {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   ON_BAILOUT(isolate, "v8::Object::HasOwnProperty()",
              return false);
   return Utils::OpenHandle(this)->HasLocalProperty(
       *Utils::OpenHandle(*key));
 }
@@ skipping 3152 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* scope_implementer =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   scope_implementer->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal