Use sender.id instead of sender.webContents.id

lib/browser/guest-window-manager.js

@@ -112,7 +112,7 @@ const getGuestWindow = function (guestId) {
 // The W3C does not have anything on this, but from my understanding of the
 // security model of |window.opener|, this should be fine.
 const canAccessWindow = function (sender, target) {
-  return (target.getWebPreferences().openerId === sender.webContents.id) ||
+  return (target.getWebPreferences().openerId === sender.id) ||
          (sender.getWebPreferences().nodeIntegration === true) ||
          isSameOrigin(sender.getURL(), target.getURL())
 }