[chrome.displaySource] Simplify session error types

extensions/common/mojo/wifi_display_session_service.mojom

 // Copyright 2015 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 extensions;
 
 // WiFiDisplaySessionService class provides access to the network for
 // the render-hosted Wi-Fi Display session.
 interface WiFiDisplaySessionService {
   SetClient(WiFiDisplaySessionServiceClient client);
 
   // Requires connection to a sink using the given authentication information.
+  // Note: 'auth_method' values must correspond to 'enum AuthenticationMethod'
+  // from display_source.idl
   Connect(int32 sink_id, int32 auth_method, string auth_data);
 
   // Drops the established connection to the connected sink.
   Disconnect();
 
   // Sends a controlling mesage to the connected sink.
   SendMessage(string message);
 };
 
 interface WiFiDisplaySessionServiceClient {
   // Notification of a successfull connection to a sink.
   OnEstablished(string ip_address);
 
   // Notification of a session termination.
   OnTerminated();
 
   // Notification of an error occurred during the session.
+  // Note: 'type' values must correspond to 'enum ErrorType'
+  // from display_source.idl
   OnError(int32 type, string description);
 
   // Invoked to transmit a controlling message from
   // the connected sink.
   OnMessage(string data);
 };