Implement RevokePermission() method in PermissionService.

content/common/permission_service.mojom

 // 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.
 
 module content;
 
 import "content/public/common/permission_status.mojom";
 
 enum PermissionName {
   GEOLOCATION,
   MIDI_SYSEX,
   NOTIFICATIONS,
   PROTECTED_MEDIA_IDENTIFIER,
 };
 
 // The Permission service provides permission handling capabilities by exposing
 // methods to check, request, and revoke permissions. It also allows a client to
 // start listening to permission changes.
 interface PermissionService {
   HasPermission(PermissionName permission, string origin)
     => (PermissionStatus status);
   RequestPermission(PermissionName permission, string origin, bool user_gesture)
     => (PermissionStatus status);
+  RevokePermission(PermissionName permission, string origin)
+    => (PermissionStatus status);
 };