chore(Docs): Add an example of extending OpaqueToken to the CHANGELOG.
chore(Docs): Add an example of extending OpaqueToken to the CHANGELOG.

PiperOrigin-RevId: 186788587

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