Don't post accessibility notification on object in detached document.

Don't post accessibility notification on object in detached document.

This can happen if an accessibility notification is queued on a node,
then that node is reparented to a different document that's not attached
anywhere before the accessibility notification is fired.

BUG=257348
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=154542

[dmazzoni, 2013-07-18 21:13:27]

I can only get a layout test to reproduce this crash if you
start content shell with the --force-renderer-accessibility flag.
It might be possible with ASAN, but I can't get a crash otherwise.

Do you think we should just check in the fix as-is? Or should I
check in a layout test that reproduces the problem when
content-side accessibility is on, just to increase coverage?

[inferno, 2013-07-18 21:21:28]

lgtm, it is ok to skip test in this case since it does not reproduce in content
shell.

[commit-bot: I haz the power, 2013-07-18 21:29:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/19768007/1

[commit-bot: I haz the power, 2013-07-19 00:00:33]

Change committed as 154542