fix(Events): event subscriptions leak and cause test failures when destroyCallbacks are empty.
fix(Events): event subscriptions leak and cause test failures when
destroyCallbacks are empty.

PiperOrigin-RevId: 161247338

matanlurey/angular,angulardart/angular,kevmoo/angular,chalin/angular2,kevmoo/angular,chalin/angular2,matanlurey/angular,matanlurey/angular,angulardart/angular,angulardart/angular,kevmoo/angular,chalin/angular2