Disable setting incognito prefs for extensions for now.

chrome/renderer/resources/extension_process_bindings.js

 // Copyright (c) 2011 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.
 
 // This script contains privileged chrome extension related javascript APIs.
 // It is loaded by pages whose URL has the chrome-extension protocol.
 
 var chrome = chrome || {};
 (function() {
   native function GetExtensionAPIDefinition();
@@ skipping 352 matching lines @@
                            [prefKey, details, callback],
                            extendSchema(setSchema));
       };
       this.clear = function(details, callback) {
         var clearSchema = this.parameters.clear;
         chromeHidden.validate([details, callback], clearSchema);
         return sendRequest('experimental.preferences.clear',
                            [prefKey, details, callback],
                            extendSchema(clearSchema));
       };
-      this.onChange = new chrome.Event('experimental.preferences.' + prefKey
-                                           + '.onChange');
+      this.onChange = new chrome.Event('experimental.preferences.'
+          + prefKey + '.onChange');
     };
     customBindings['Preference'].prototype = new CustomBindingsObject();
   }
 
   // Page action events send (pageActionId, {tabId, tabUrl}).
   function setupPageActionEvents(extensionId) {
     var pageActions = GetCurrentPageActions(extensionId);
 
     var oldStyleEventName = "pageActions";
     // TODO(EXTENSIONS_DEPRECATED): only one page action
@@ skipping 522 matching lines @@
 
   if (!chrome.experimental)
     chrome.experimental = {};
 
   if (!chrome.experimental.accessibility)
     chrome.experimental.accessibility = {};
 
   if (!chrome.experimental.tts)
     chrome.experimental.tts = {};
 })();