Object.getOwnPropertyDescriptors: add test to ensure undefined desc…

…riptors are not added.

Per tc39/ecma262#593

test/built-ins/Object/getOwnPropertyDescriptors/proxy-undefined-descriptor.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2016 Jordan Harband. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Object.getOwnPropertyDescriptors should perform observable operations in the correct order
+esid: sec-object.getownpropertydescriptors
+author: Jordan Harband
+features: [Proxy]
+includes: [proxyTrapsHelper.js]
+---*/
+
+var key = "a";
+var ownKeys = [key];
+var badProxyHandlers = allowProxyTraps({
+  getOwnPropertyDescriptor: function () {},
+  ownKeys: function () {
+	return ownKeys;
+  }
+});
+var proxy = new Proxy({}, badProxyHandlers);
+
+var keys = Object.keys(proxy);
+assert.sameValue(keys, ownKeys, 'Object.keys returns the result of the [[OwnKeys]] trap');
+
+var descriptor = Object.getOwnPropertyDescriptor(proxy, key);
+assert.sameValue(descriptor, undefined, "Descriptor matches result of [[GetOwnPropertyDescriptor]] trap");
+
+var result = Object.getOwnPropertyDescriptors(proxy);
+assert.sameValue(key in result, false, "key is not present in result")