Permissions: use newly supported required attribute on Dictionary properties.

Source/modules/permissions/PermissionDescriptor.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 enum PermissionName {
     "geolocation",
     "midi",
     "notifications",
     "push"
 };
 
 // The PermissionDescriptor dictionary is a base to describe permissions. Some
 // permissions will extend it. The methods reading it will re-parse it depending
 // on the name.
 dictionary PermissionDescriptor {
-    /* required */ PermissionName name;
+    required PermissionName name;
 };