Ensure keymessage response to generateKeyRequest() has keySystem set for external CDMs.

content/test/data/media/encrypted_media_utils.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.
 
 var QueryString = function() {
   // Allows access to query parameters on the URL; e.g., given a URL like:
   //    http://<server>/my.html?test=123&bob=123
   // Parameters can then be accessed via QueryString.test or QueryString.bob.
   var params = {};
   // RegEx to split out values by &.
@@ skipping 99 matching lines @@
     catch(error) {
       setDocTitle("GenerateKeyRequestException");
     }
   }
 
   function onKeyAdded(e) {
     e.target.receivedKeyAdded = true;
   }
 
   function onKeyMessage(e) {
-    // TODO(ddorwin): Enable after fixing http://crbug.com/166204.
-    if (!e.keySystem && false) {
+    if (!e.keySystem) {
       failTest('keymessage without a keySystem: ' + e.keySystem);
       return;
     }
 
     if (!e.sessionId) {
       failTest('keymessage without a sessionId: ' + e.sessionId);
       return;
     }
 
     if (!e.message) {
@@ skipping 37 matching lines @@
   mediaSource.addEventListener('webkitsourceopen', onSourceOpen);
   video.addEventListener('webkitneedkey', onNeedKey);
   video.addEventListener('webkitkeymessage', onKeyMessage);
   video.addEventListener('webkitkeyerror', failTest);
   video.addEventListener('webkitkeyadded', onKeyAdded);
   installTitleEventHandler(video, 'error');
 
   video.src = window.URL.createObjectURL(mediaSource);
   return mediaSource;
 }