Implement basic mojo Permission service and use it for Geolocation.

content/common/permission_service.mojom

Index: content/common/permission_service.mojom
diff --git a/content/common/permission_service.mojom b/content/common/permission_service.mojom
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+++ b/content/common/permission_service.mojom
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+// 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;
+};
+
+// 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);
+};