createAnimationController method
Called to create the animation controller that will drive the transitions to this route from the previous one, and back to the previous route from this one.
Implementation
AnimationController createAnimationController() {
assert(!_transitionCompleter.isCompleted, 'Cannot reuse a $runtimeType after disposing it.');
final Duration duration = transitionDuration;
assert(duration != null && duration >= Duration.zero);
return AnimationController(
duration: duration,
debugLabel: debugLabel,
vsync: navigator,
);
}