<webview>: First stab at implementing media permission request for guests.

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', 'partition'];
@@ skipping 102 matching lines @@
         return objectNode[attributeName];
       },
       // No setter.
       enumerable: true
     })
   }, this);
 
   for (var eventName in WEB_VIEW_EVENTS) {
     this.setupEvent_(eventName, WEB_VIEW_EVENTS[eventName]);
   }
+  this.maybeSetupPermissionEvent_();
 }
 
 /**
  * @private
  */
 WebView.prototype.handleMutation_ = function(mutation) {
   this.node_[mutation.attributeName] =
       this.node_.getAttribute(mutation.attributeName);
 };
 
 /**
  * @private
  */
-WebView.prototype.setupEvent_ = function(eventname, attribs) {
+WebView.prototype.setupEvent_ = function(eventname, attribs, opt_prepareEvent) {
   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] = detail[attribName];
     });
+    if (opt_prepareEvent) {
+      opt_prepareEvent(evt, detail);
+    }
     node.dispatchEvent(evt);
   });
-}
+};
+
+/**
+ * Implemented when webview.permissionAPI permission is available.
+ * @private
+ */
+WebView.prototype.maybeSetupPermissionEvent_ = function() {};
+
+exports.WebView = WebView;