[webkit-dev] Disallowing modal dialogs during unload events

[Sreeram Ramachandran]

We'd like to disallow modal dialogs (i.e., those arising from calls to
alert, confirm, prompt or showModalDialog) during unload events
(beforeunload, unload and pagehide) [1]. Chromium wants to do this
[2]. Since this affects web compatibility, I'd like to get agreement
from the other webkit ports as well.

The benefits are:
+ Fewer annoyances for users who are trying to leave a page.
+ In the case of tab close, allows the browser to hide the tab before
it has finished running the unload or pagehide event handlers (doesn't
apply to beforeunload); gives the impression of better performance.

This doesn't affect returning a non-null value from beforeunload; that
will still cause the browser to show the stay-or-leave dialog. We
think that is sufficient to satisfy legitimate needs to warn the user
about data loss, etc.

Outside webkit, this has been discussed on whatwg, but without a
definite conclusion [3]. Firefox seems to be considering this as well
[4].

All in favour, say aye!

[1] https://bugs.webkit.org/show_bug.cgi?id=56397
[2] http://code.google.com/p/chromium/issues/detail?id=68780
[3] http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2010-February/025080.html
[4] https://bugzilla.mozilla.org/show_bug.cgi?id=391834