Notifications API is not covered by Zone.js

[marcovdb]

The Notifications API is not covered by Zone.js - meaning, if I initiate a notification from a zone and attach an function to the notification's onclick event, this function is not executed in the current zone.

I originally opened this as an Angular issue (angular/angular#12624) but I was asked to reopen it here, so here goes.

[JiaLiPassion]

Sure, several other apis are not in zone now, I would like to make a pr to implement it.