[proxies] Use JSReceiver::GetKeys() for more purposes

test/mjsunit/harmony/proxies-for.js

 // Copyright 2011 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 124 matching lines @@
 (function() {
   var p = new Proxy({}, {enumerate:function() { return ["0"].values(); }});
   var o = [0];
   o.__proto__ = p;
   var keys = [];
   for (var k in o) { keys.push(k); };
   assertEquals(["0"], keys);
 })();
 
 (function () {
-  var p = new Proxy({}, {getOwnPropertyNames:
-    function() { return [1, Symbol(), 2] }});
+  var p = new Proxy({}, {ownKeys: function() { return ["1", Symbol(), "2"] }});
   assertEquals(["1","2"], Object.getOwnPropertyNames(p));
 })();