Way to determine the render context on the fly

[bluepnume]

There are situations where we need to figure out what render context we want to use, on the fly in the parent page.

For example: for PayPal Checkout, if the user is one-touch logged in, we render checkout in a lightbox iframe, otherwise we use a popup window.

One possibility is to add a method like:

determineContext() {
    return someContextDeterminingPromise();
}

The only problem with this is it begins to add runnable code / logic to the parent page, which I'm not sure if we want to do for xcomponent

[bluepnume]

Probably best if we just allow people to mutate Component.contexts for now in an async way, if they want. Anything else is just going to be too complicated given that we always need to open popup windows synchronously on button click.