Improve Proxy/ownKeys invariants coverage (#2384)

* Add non-configurable invariant test

* Add non-extensible invariant test

test/built-ins/Object/keys/proxy-non-enumerable-prop-invariant-1.js

@@ -0,0 +1,54 @@
+// Copyright (C) 2019 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-object.keys
+description: >
+  Proxy [[OwnPropertyKeys]] trap does not skip non-enumerable keys when validating invariant:
+  * The result List must contain the keys of all non-configurable own properties of
+    the target object.
+info: |
+  Object.keys ( O )
+
+  ...
+  2. Let nameList be ? EnumerableOwnPropertyNames(obj, "key").
+
+  EnumerableOwnPropertyNames ( O, kind )
+
+  ...
+  2. Let ownKeys be ? O.[[OwnPropertyKeys]]().
+
+  [[OwnPropertyKeys]] ( )
+
+  ...
+  11. Let targetKeys be ? target.[[OwnPropertyKeys]]().
+  ...
+  15. Let targetNonconfigurableKeys be a new empty List.
+  16. For each element key of targetKeys, do
+    a. Let desc be ? target.[[GetOwnProperty]](key).
+    b. If desc is not undefined and desc.[[Configurable]] is false, then
+      i. Append key as an element of targetNonconfigurableKeys.
+  ...
+  18. Let uncheckedResultKeys be a new List which is a copy of trapResult.
+  19. For each key that is an element of targetNonconfigurableKeys, do
+    a. If key is not an element of uncheckedResultKeys, throw a TypeError exception.
+features: [Proxy]
+---*/
+
+var target = {};
+Object.defineProperty(target, 'prop', {
+  value: 1,
+  writable: true,
+  enumerable: false,
+  configurable: false,
+});
+
+var proxy = new Proxy(target, {
+  ownKeys: function() {
+    return [];
+  },
+});
+
+assert.throws(TypeError, function() {
+  Object.keys(proxy);
+});

test/built-ins/Object/keys/proxy-non-enumerable-prop-invariant-2.js

@@ -0,0 +1,56 @@
+// Copyright (C) 2019 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-object.keys
+description: >
+  Proxy [[OwnPropertyKeys]] trap does not skip non-enumerable keys when validating invariant:
+  * If the target object is not extensible, then the result List must contain all the keys of
+    the own properties of the target object and no other values.
+info: |
+  Object.keys ( O )
+
+  ...
+  2. Let nameList be ? EnumerableOwnPropertyNames(obj, "key").
+
+  EnumerableOwnPropertyNames ( O, kind )
+
+  ...
+  2. Let ownKeys be ? O.[[OwnPropertyKeys]]().
+
+  [[OwnPropertyKeys]] ( )
+
+  ...
+  11. Let targetKeys be ? target.[[OwnPropertyKeys]]().
+  16. For each element key of targetKeys, do
+    a. Let desc be ? target.[[GetOwnProperty]](key).
+    b. If desc is not undefined and desc.[[Configurable]] is false, then
+      ...
+    c. Else,
+      i. Append key as an element of targetConfigurableKeys.
+  ...
+  18. Let uncheckedResultKeys be a new List which is a copy of trapResult.
+  ...
+  21. For each key that is an element of targetConfigurableKeys, do
+    a. If key is not an element of uncheckedResultKeys, throw a TypeError exception.
+features: [Proxy]
+---*/
+
+var target = {};
+Object.defineProperty(target, 'prop', {
+  value: 2,
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});
+Object.preventExtensions(target);
+
+var proxy = new Proxy(target, {
+  ownKeys: function() {
+    return [];
+  },
+});
+
+assert.throws(TypeError, function() {
+  Object.keys(proxy);
+});