Clarifies the timing of updates to `Router.current`
Clarifies the timing of updates to `Router.current`

PiperOrigin-RevId: 190639901

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