[es6] Fix Object built-in subclassing.

src/js/v8natives.js

 // Copyright 2012 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.
 
 (function(global, utils) {
 
 %CheckIsBootstrapping();
 
 // ----------------------------------------------------------------------------
 // Imports
@@ skipping 1293 matching lines @@
 // ECMA-262, Edition 6, section B.2.2.1.2
 function ObjectSetProto(proto) {
   CHECK_OBJECT_COERCIBLE(this, "Object.prototype.__proto__");
 
   if ((IS_SPEC_OBJECT(proto) || IS_NULL(proto)) && IS_SPEC_OBJECT(this)) {
     %SetPrototype(this, proto);
   }
 }
 
 
+// ECMA-262, Edition 6, section 19.1.1.1
 function ObjectConstructor(x) {
-  if (%_IsConstructCall()) {
-    if (x == null) return this;
-    return TO_OBJECT(x);
-  } else {
-    if (x == null) return { };
-    return TO_OBJECT(x);
+  if (GlobalObject != new.target && !IS_UNDEFINED(new.target)) {
+    return this;
   }
+  if (IS_NULL(x) || IS_UNDEFINED(x)) return {};
+  return TO_OBJECT(x);
 }
 
 
 // ----------------------------------------------------------------------------
 // Object
 
 %SetNativeFlag(GlobalObject);
 %SetCode(GlobalObject, ObjectConstructor);
 
 %AddNamedProperty(GlobalObject.prototype, "constructor", GlobalObject,
@@ skipping 517 matching lines @@
 
 %InstallToContext([
   "global_eval_fun", GlobalEval,
   "object_value_of", ObjectValueOf,
   "object_to_string", ObjectToString,
   "object_get_own_property_descriptor", ObjectGetOwnPropertyDescriptor,
   "to_complete_property_descriptor", ToCompletePropertyDescriptor,
 ]);
 
 })