[builtins] don't create keys for undefined property descriptors in O.gOPDs

test/mjsunit/harmony/object-get-own-property-descriptors.js

 // Copyright 2016 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.
 
 // Flags: --harmony-object-own-property-descriptors
 // Flags: --allow-natives-syntax
 
 function DataDescriptor(value) {
   return { "enumerable": true, "configurable": true, "writable": true, value };
 }
@@ skipping 177 matching lines @@
         value: "VALUE"
       };
     },
     get(target, name) { assertUnreachable(); },
     set(target, name, value) { assertUnreachable(); },
     deleteProperty(target, name) { assertUnreachable(); },
     defineProperty(target, name, desc) { assertUnreachable(); }
   });
 
   var result = Object.getOwnPropertyDescriptors(P);
-  assertEquals({ "A": undefined }, result);
+  assertEquals({
+    "A": {
+      "value": "VALUE",
+      "writable": false,
+      "enumerable": false,
+      "configurable": true
+    }
+  }, result);
   assertTrue(result.hasOwnProperty("A"));
   assertEquals([
     "ownKeys()",
     "getOwnPropertyDescriptor(A)",
     "getOwnPropertyDescriptor(A)"
   ], log);
 }
 TestDuplicateKeys();
+
+function TestFakeProperty() {
+  var log = [];
+  var P = new Proxy({}, {
+    ownKeys() {
+      log.push(`ownKeys()`);
+      return ["fakeProperty"];
+    },
+    getOwnPropertyDescriptor(target, name) {
+      log.push(`getOwnPropertyDescriptor(${name})`);
+      return;
+    }
+  });
+  var result = Object.getOwnPropertyDescriptors(P);
+  assertEquals({}, result);
+  assertFalse(result.hasOwnProperty("fakeProperty"));
+  assertEquals([
+    "ownKeys()",
+    "getOwnPropertyDescriptor(fakeProperty)"
+  ], log);
+}
+TestFakeProperty();