[proxies] allow duplicate keys for [[OwnPropertyKeys]] trap.

test/mjsunit/harmony/proxies-ownkeys.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.
 
 // Flags: --harmony-proxies --harmony-reflect
 
 var target = {
   "target_one": 1
 };
 target.__proto__ = {
@@ skipping 38 matching lines @@
 assertEquals([], Reflect.ownKeys(proxy));
 keys.length = 1;
 assertEquals(["a"], Reflect.ownKeys(proxy));
 keys.length = 3;
 assertEquals(["a", "b", "c"], Reflect.ownKeys(proxy));
 // The spec wants to allow lengths up to 2^53, but we can't allocate arrays
 // of that size, so we throw even for smaller values.
 keys.length = Math.pow(2, 33);
 assertThrows("Reflect.ownKeys(proxy)", RangeError);
 
+// Check that we allow duplicated keys.
+keys  = ['a', 'a', 'a']
+assertEquals(keys, Reflect.ownKeys(proxy));
+
 // Non-Name results throw.
 keys = [1];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 keys = [{}];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 keys = [{toString: function() { return "foo"; }}];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 keys = [null];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 
 // Step 17a: The trap result must include all non-configurable keys.
 Object.defineProperty(target, "nonconf", {value: 1, configurable: false});
 keys = ["foo"];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 keys = ["nonconf"];
 assertEquals(keys, Reflect.ownKeys(proxy));
 
+// Check that we allow duplicated keys.
+keys  = ['nonconf', 'nonconf', 'nonconf']
+assertEquals(keys, Reflect.ownKeys(proxy));
+
 // Step 19a: The trap result must all keys of a non-extensible target.
 Object.preventExtensions(target);
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
 keys = ["nonconf", "target_one"];
 assertEquals(keys, Reflect.ownKeys(proxy));
 
 // Step 20: The trap result must not add keys to a non-extensible target.
 keys = ["nonconf", "target_one", "fantasy"];
 assertThrows("Reflect.ownKeys(proxy)", TypeError);
+
+// Check that we allow duplicated keys.
+keys  = ['nonconf', 'target_one', 'nonconf', 'nonconf', 'target_one',]
+assertEquals(keys, Reflect.ownKeys(proxy));