Write tests for roles dialog and alertdialog ATK's window interface #260

See conversation starting here: w3c/aria#2808 (comment)

The WPT aamtests test ATSPI. To check if the "window" interface is implemented on the ATK side, I think we can check whether the correct events are triggered:

AT-SPI listens for the ATK events and passes (most of) them to assistive technologies. See this code.

At the time of this writing, the aamtests don't support events, but hopefully they will soon!