6049 add support for onCancel event

[ludvigsen]

Adds support for the onCancel event described here: #6049

[facebook-github-bot]

@ludvigsen updated the pull request.

[facebook-github-bot]

@ludvigsen updated the pull request.

[cbrwizard]

This might not be needed at all, but I think that this change will benefit from tests. Like in this file.

[ludvigsen]

@cbrwizard I don't think jsdom supports the Dialog element, so testing this could prove an issue, at least through jsdom/jest.

[NoelBroda]

@ludvigsen ping

[vcanales]

@ludvigsen I took your code, rebased and fixed conflicts. I don't know if it helps but I'd at least like to give this issue a bit of visibility.

vcanales@1bca7a6

[ludvigsen]

@devjunkORG Thanks, I appreciate it. Did you check to see if stuff still works as well?

[aweary]

@ludvigsen looks like there are a number of conflicts. Would you be able to resolve those? I'd like to make sure this gets in.

[ludvigsen]

@aweary Great! I'll try to resolve the conflicts.

[ludvigsen]

@aweary Resolved the conflicts also added onClose event for completeness

[aweary]

Thanks @ludvigsen! I verified locally that the events are being dispatched for onClose and onCancel with a <dialog /> element. This LGTM, thanks again!