Support WebSocket in WebRequest API.

chrome/test/data/extensions/api_test/webrequest/test_types.js

 // 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.
 
 function getStyleURL() {
   // This is not a style sheet, but it must still be classified as "stylesheet"
   // because it is loaded as a style sheet.
   return getServerURL('empty.html?as-style');
 }
 
@@ skipping 592 matching lines @@
 
     var frame = document.createElement('iframe');
     document.body.appendChild(frame);
     frame.contentWindow.onunload = function() {
       console.log('Going to send beacon...');
       var sentBeacon = frame.contentWindow.navigator.sendBeacon(getSlowURL());
       chrome.test.assertTrue(sentBeacon);
     };
     frame.remove();
   },
+
+  // Note: The 'websocket' type is tested separately in 'test_websocket.js'.
 ]);