browser-plugin: Send a JSON string for the detail data with the events.

chrome/renderer/resources/extensions/web_view.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.
 
 // Shim that simulates a <webview> tag via Mutation Observers.
 //
 // The actual tag is implemented via the browser plugin. The internals of this
 // are hidden via Shadow DOM.
 
 var WEB_VIEW_ATTRIBUTES = ['src'];
@@ skipping 139 matching lines @@
       attributeName, this.node_.getAttribute(attributeName));
 };
 
 /**
  * @private
  */
 WebView.prototype.setupEvent_ = function(eventname, attribs) {
   var node = this.node_;
   this.objectNode_.addEventListener('-internal-' + eventname, function(e) {
     var evt = new Event(eventname);
+    var detail = e.detail ? JSON.parse(e.detail) : {};
     attribs.forEach(function(attribname) {
-      evt[attribname] = e.detail[attribname];
+      evt[attribname] = detail[attribname];
     });
     node.dispatchEvent(evt);
   });
 }