[snack-bar] onAction subject never completes

[willshowell]

Bug, feature request, or proposal:

Bug

What is the current behavior?

Subscribing to onAction() will result in a subscription that never completes unless the action button is clicked.

Expected behavior

onAction() completes when the snackbar ref is destroyed, I suppose in _finishDismiss().

Reproduction

https://stackblitz.com/edit/angular-material2-issue-l1ymh2?file=app/app.component.ts

Motivation

I wish to open a snack-bar that has a duration longer than the expected lifetime of the component opening it. When the action is clicked, I would like to navigate to a new route.

I am unable to unsubscribe from the subscription in ngOnDestroy since the snackbar action may be available after the component is destroyed.

[AsserHamad]

There appears to already be a method which fires an action once the snackbar is destroyed (afterDismissed), but right now there's nothing to replace the old onAction command

[crisbeto]

onAction is still there.

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