[es6] Implement Reflect.enumerate.

src/js/harmony-reflect.js

-// Copyright 2013 the V8 project authors. All rights reserved.
+// Copyright 2013-2015 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) {
 
 'use strict';
 
 %CheckIsBootstrapping();
 
 var GlobalReflect = global.Reflect;
 var ReflectApply = utils.ImportNow("reflect_apply");
 var ReflectConstruct = utils.ImportNow("reflect_construct");
 
+function ReflectEnumerate(obj) {
+  if (!IS_SPEC_OBJECT(obj))
+    throw MakeTypeError(kCalledOnNonObject, "Reflect.enumerate")
+  return (function* () { for (var x in obj) yield x })();
+}
+
 utils.InstallFunctions(GlobalReflect, DONT_ENUM, [
   "apply", ReflectApply,
-  "construct", ReflectConstruct
+  "construct", ReflectConstruct,
+  "enumerate", ReflectEnumerate
 ]);
 
 })