Notification when aborted -> retried transition completes

[sandstrom]

For regular transitions, using the then method on the returned Transition works well. When the transition is completed then callback is called.

With aborted + retried transitions it's trickier. Since retry creates a new transition (code below), it isn't possible to get notified when it resolves.

1. Is this by design?
2. If not, would it be possible to improve this?

Copying over the transition would work, but may break things (I don't know). Another option would be to introduce another method, something like retryableThen() on Promise, whose underlying promise would get copied over to retried transitions.

What are your thoughts? (cc: @asakusuma @chadhietala)

retry() {
    this.abort();
    let newTransition = this.router.transitionByIntent(this.intent as OpaqueIntent, false);

    // [...] shortened for clarity
    return newTransition;
  }

Source: https://github.com/tildeio/router.js/blob/c82c0ca1b7/lib/router/transition.ts#L273