Improve curtain mode error message.

remoting/webapp/client_screen.js

 // Copyright (c) 2012 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.
 
 /**
  * @fileoverview
  * Functions related to the 'client screen' for Chromoting.
  */
 
 'use strict';
@@ skipping 237 matching lines @@
     if (oldState == remoting.ClientSession.State.CONNECTED) {
       remoting.clientSession.removePlugin();
       remoting.clientSession = null;
       console.log('Connection closed by host');
       if (remoting.currentConnectionType == remoting.ConnectionType.It2Me) {
         remoting.setMode(remoting.AppMode.CLIENT_SESSION_FINISHED_IT2ME);
       } else {
         remoting.setMode(remoting.AppMode.CLIENT_SESSION_FINISHED_ME2ME);
       }
     } else {
-      // The transition from CONNECTING to CLOSED state may happen
-      // only with older client plugins. Current version should go the
-      // FAILED state when connection fails.
-      showConnectError_(remoting.Error.INVALID_ACCESS_CODE);
+      // A state transition from CONNECTING -> CLOSED can happen if the host
+      // closes the connection without an error message instead of accepting it.
+      // For example, it does this if it fails to activate curtain mode. Since
+      // there's no way of knowing exactly what went wrong, we rely on server-
+      // side logs in this case and show a generic error message.
+      showConnectError_(remoting.Error.UNEXPECTED);
     }
 
   } else if (newState == remoting.ClientSession.State.FAILED) {
     console.error('Client plugin reported connection failed: ' +
                   remoting.clientSession.error);
     clearPin = true;
     if (remoting.clientSession.error ==
         remoting.ClientSession.ConnectionError.HOST_IS_OFFLINE) {
       clearPin = false;
       retryConnectOrReportOffline_();
@@ skipping 277 matching lines @@
             remoting.ClientSession.Mode.ME2ME, onClientStateChange_);
     // Don't log errors for cached JIDs.
     remoting.clientSession.logErrors(!remoting.retryIfOffline);
     remoting.clientSession.createPluginAndConnect(
         document.getElementById('session-mode'),
         token);
   } else {
     showConnectError_(remoting.Error.AUTHENTICATION_FAILED);
   }
 }