Move Object.assign implementation to C++

src/js/prologue.js

 // Copyright 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, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 183 matching lines @@
     "MapIterator",
     "MapIteratorNext",
     "MathMax",
     "MathMin",
     "MaxSimple",
     "MinSimple",
     "ObjectIsFrozen",
     "ObjectDefineProperty",
     "ObserveArrayMethods",
     "ObserveObjectMethods",
-    "OwnPropertyKeys",
     "PromiseChain",
     "PromiseDeferred",
     "PromiseResolved",
     "SameValueZero",
     "SetIterator",
     "SetIteratorNext",
     "SetValues",
     "SymbolToString",
     "ToPositiveInteger",
     // From runtime:
@@ skipping 130 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg) {
     return %Apply(func, thisArg, arguments, 1, arguments.length - 1);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })