Decide based on whether or not a event has an own `currentTarget`. (...)
Decide based on whether or not a event has an own `currentTarget`. (...)

Safari 9 both doesn't have working `Event.prototype` descriptors and doesn't
allow event property getter / function call context objects to be anything other
than exactly the original event, so `utils.settings.hasDescriptors` is not a
sufficient basis for deciding whether or not to use the proxy-like event object
wrapper.

webcomponents/polyfills,webcomponents/polyfills,webcomponents/polyfills