blink: permissions: add plumbing to request permissions

Source/modules/permissions/Permissions.idl

 // Copyright 2014 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.
 
 // Specification at:
 // https://w3c.github.io/permissions/
 
 [
     Exposed=(Window,Worker),
     GarbageCollected,
     RuntimeEnabled=Permissions
 ] interface Permissions {
     [CallWith=ScriptState, Measure] Promise<PermissionStatus> query(object permission);
+    [RuntimeEnabled=PermissionsRequestRevoke, CallWith=ScriptState, Measure] Promise<PermissionStatus> request(object permission);
     [RuntimeEnabled=PermissionsRequestRevoke, CallWith=ScriptState, Measure] Promise<PermissionStatus> revoke(object permission);
 };