Switch PermissionStatus events to an observer model.

third_party/WebKit/public/platform/modules/permissions/permission.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 blink.mojom;
 
 import "third_party/WebKit/public/platform/modules/permissions/permission_status.mojom";
 import "url/mojo/origin.mojom";
 
 enum PermissionName {
@@ skipping 17 matching lines @@
   MidiPermissionDescriptor midi;
 };
 
 // This struct roughly corresponds to the PermissionDescriptor dictionary as
 // defined by the Permissions API.
 struct PermissionDescriptor {
   PermissionName name;
   PermissionDescriptorExtension? extension;
 };
 
+// Interface a client can implement to observe permission changes.
+interface PermissionObserver {
+  OnPermissionStatusChange(PermissionStatus status);
+};
+
 // 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(PermissionDescriptor permission, url.mojom.Origin origin)
     => (PermissionStatus status);
   RequestPermission(PermissionDescriptor permission, url.mojom.Origin origin,
       bool user_gesture)
     => (PermissionStatus status);
   RequestPermissions(array<PermissionDescriptor> permission, url.mojom.Origin origin,
       bool user_gesture)
     => (array<PermissionStatus> statuses);
   RevokePermission(PermissionDescriptor permission, url.mojom.Origin origin)
     => (PermissionStatus status);
-
-  // Runs the callback next time there is a permission status change for the
-  // given { permission, origin }. Callers of this method will have to call it
-  // again if they want to keep listening to the changes. To prevent race
-  // conditions, the caller must pass the last known value.
-  GetNextPermissionChange(PermissionDescriptor permission,
-                          url.mojom.Origin origin,
-                          PermissionStatus last_known_status)
-    => (PermissionStatus status);
+  AddPermissionObserver(PermissionDescriptor permission,

[mlamouri (slow - plz ping), 2016/12/19 13:37:45]

It would be good to add a comment. You should be able to re-use most of what you
removed above. Also, can you explain that the observe will be auto-removed when
the connection drops? There is no `RemovePermissionObserver` and at a first
glance it's unclear if it's on purpose or a bug.

[Reilly Grant (use Gerrit), 2016/12/19 22:23:59]

Done.

+                        url.mojom.Origin origin,
+                        PermissionStatus last_known_status,
+                        PermissionObserver observer);
 };