Three uses of new Function[1][2][3] for custom event handling in preferencesBindings.js need to be removed as part of Bug 1473549.

[1] https://searchfox.org/mozilla-central/source/toolkit/content/preferencesBindings.js#238

[2] https://searchfox.org/mozilla-central/source/toolkit/content/preferencesBindings.js#350

[3] https://searchfox.org/mozilla-central/source/toolkit/content/preferencesBindings.js#408

I would like to eliminate these three new Functions, which are used to evaluate event handling code from XUL-attributes, namely:

onbeforeaccept
onsyncfrompreference
onsynctopreference

The first is easily removed and replaced by JS-eventListeners, but the other two look more complicated.
In both cases, the code invoked upon the respective events returns values other than true/false that are processed further. I don't see an immediate way to replicate this behaviour with eventListeners.
What could be a reasonable approach here?

https://searchfox.org/mozilla-central/source/toolkit/content/preferencesBindings.js#345

https://searchfox.org/mozilla-central/source/toolkit/content/preferencesBindings.js#403

Defining a "manual" JS callback/observer infrastructure in preferencesBinding.js that JS on the page can add callbacks/observers to that behave how we want (ie we use returned values if not undefined, or something) seems like the most straightforward way. There's no real need to actually use custom events.

Work in progress.
Add callback infrastructure to preferenceBindings to replace XUL-attributes.

Jorg, heads-up that we're killing onsync{to,from}preference here. I expect thunderbird might care... I also don't think this will land in soft freeze, so probably early (ish?) in the 70 cycle.

Thanks for the heads-up, forwarding ...

Filed bug 1562560 for thunderbird.

Umm, what about comment #4. Not landing during soft freeze, which is now. I'll remove the checkin-needed again, no offence intended.

Right, sorry. I missed that, no offence taken.

Jonas, this needs a rebase now (probably due to the prettier changes). Can you rebase and upload the updated version? Sorry for the churn...

I rebased the patch. Should I flag checkin-needed now?

Sure, sorry, for the extra hassle.

Pushed by opoprus@mozilla.com:
https://hg.mozilla.org/integration/autoland/rev/d426669c4cba
Remove preferenceBindings.js from eval()-whitelist, r=Gijs

https://hg.mozilla.org/mozilla-central/rev/d426669c4cba