DebugContext.component returns null instead of throwing for Visibility.none
DebugContext.component returns null instead of throwing for Visibility.none

This is done to support a common testing pattern using DebugNode.query where a
predicate invoking DebugContext.component is used to locate a specific component
instance.

PiperOrigin-RevId: 166720982

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