Snackbar does not always dismiss when activated via keyboard

[yuheiy]

What MDC-Web Version are you using?

0.28.0

What browser(s) is this bug affecting?

Chrome/63.0.3239.132 (also others)

What OS are you using?

Mac OS X 10_13_2

What are the steps to reproduce the bug?

If I operate the radio button with the keyboard, snackbar will not work properly.

1. Go to https://jsfiddle.net/yuheiy/d1e0j490/
2. Operate the radio button with the keyboard
3. Snackbar will not be hidden

[acdvorak]

Thanks for filing this issue!

It looks like there's something wrong with the focus handling logic in the foundation.

The cleanup_() method checks the value of snackbarHasFocus_, which should (I think) be false, but for some reason it's true.

It might be a problem with handlePossibleTabKeyboardFocus_ and/or setFocusOnAction_, but I'm not sure - we'll need to investigate.

[piotr-cz]

Problem is that during time when snackbar is opened, focusing any element is evaluated by the library as focusing action button and so library keeps snackbar element opened.

Another steps to reproduce:

1. Go to https://material-components-web.appspot.com/snackbar.html
2. Delete Action Text value
3. Click on Show
4. Press Shift-Tab to focus some element on the page (like Action Text input element)

Snackbar should close, but it doesn't.