fix test to work with strong mode checking of mock classes, by adding an abstract `doesNotExist` property so we can access it.
fix test to work with strong mode checking of mock classes, by adding an abstract `doesNotExist` property so we can access it.

(also removes @proxy because this no longer has any effect in strong mode, having `noSuchMethod` is enough.)

PiperOrigin-RevId: 162946111

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