Implement chrome.downloads.onDeterminingFilename()

chrome/renderer/resources/extensions/web_request_custom_bindings.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.
 
 // Custom bindings for the webRequest API.
 
 var webRequestNatives = requireNative('web_request');
 var GetUniqueSubEventName = webRequestNatives.GetUniqueSubEventName;
 
 var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
@@ skipping 41 matching lines @@
 };
 
 // Registers a callback to be called when this event is dispatched. If
 // opt_filter is specified, then the callback is only called for events that
 // match the given filters. If opt_extraInfo is specified, the given optional
 // info is sent to the callback.
 WebRequestEvent.prototype.addListener =
     function(cb, opt_filter, opt_extraInfo) {
   if (!this.eventOptions_.supportsListeners)
     throw new Error('This event does not support listeners.');
+  // NOTE(benjhayden) New APIs should not use this subEventName trick! It does
+  // not play well with event pages. See downloads.onDeterminingFilename and
+  // ExtensionDownloadsEventRouter for an alternative approach.
   var subEventName = GetUniqueSubEventName(this.eventName_);
   // Note: this could fail to validate, in which case we would not add the
   // subEvent listener.
   validate(Array.prototype.slice.call(arguments, 1), this.extraArgSchemas_);
   chromeHidden.internalAPIs.webRequestInternal.addEventListener(
       cb, opt_filter, opt_extraInfo, this.eventName_, subEventName);
 
   var subEvent = new chrome.Event(subEventName, this.argSchemas_);
   var subEventCallback = cb;
   if (opt_extraInfo && opt_extraInfo.indexOf('blocking') >= 0) {
@@ skipping 78 matching lines @@
 
 chromeHidden.registerCustomHook('webRequest', function(api) {
   var apiFunctions = api.apiFunctions;
 
   apiFunctions.setHandleRequest('handlerBehaviorChanged', function() {
     var args = Array.prototype.slice.call(arguments);
     sendRequest(this.name, args, this.definition.parameters,
                 {forIOThread: true});
   });
 });