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,
+};
+
+struct Permission {
+  PermissionName name;

[blundell, 2014/11/14 08:29:20]

What is the reason for the existence of the Permission struct? If you're
anticipating adding more things besides the name, I would suggest delaying until
it's actually needed unless that's in a short-term followup.

[mlamouri (slow - plz ping), 2014/11/14 11:37:11]

Done.

+};
+
+// 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.
+[Client=PermissionServiceClient]
+interface PermissionService {
+  HasPermission(Permission permission, string origin)
+    => (PermissionStatus status);
+  RequestPermission(Permission permission, string origin)
+    => (PermissionStatus status);
+  RevokePermission(Permission permission, string origin)
+    => (PermissionStatus status);
+
+  StartObserving(Permission permission, string origin);
+  StopObserving(Permission permission, string origin);
+};
+
+interface PermissionServiceClient {
+  OnPermissionChange(Permission permission,
+                     string origin,
+                     PermissionStatus status);
+};