Implement basic mojo Permission service and use it for Geolocation.

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;
+
+enum PermissionStatus {
+  GRANTED,
+  DENIED,
+  ASK
+};
+
+enum PermissionName {
+  GEOLOCATION,
+};
+
+// 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 {
+  QueryPermission(PermissionName permission, string origin)
+    => (PermissionStatus status);
+  RequestPermission(PermissionName permission, string origin)
+    => (PermissionStatus status);
+//   RevokePermission(PermissionName permission, string origin)
+//     => (PermissionStatus status);
+
+//  StartObserving(PermissionName permission, string origin);
+//  StopObserving(PermissionName permission, string origin);
+};
+
+// interface PermissionServiceClient {
+//   OnPermissionChange(PermissionName permission,
+//                      string origin,
+//                      PermissionStatus status);
+// };