DOM Events Proposal: EventListenerOptions 'mayCancel' for improved scroll performance

In Chromium we've long struggled with maximizing scroll performance, with
scroll-blocking DOM events (wheel and touchstart in particular) being by
far the biggest source of scroll jank.

I've been talking about this problem off-and-on for several years with
various folks including the Pointer Events Working Group, engineers of
other browser vendors, and engineers working on popular libraries that are
a source of such scroll-blocking event handlers (eg. Google Ads and
Google Analytics).

I've now written a relatively formal (but still sloppy by W3C standards)
concrete spec for extending the DOM event model
<http://rbyers.github.io/EventListenerOptions/EventListenerOptions.html> to
address this problem and would like to solicit feedback.  It's probably
most constructive to discuss specific issues on GitHub
<https://github.com/RByers/EventListenerOptions/issues>, but I'd appreciate
any high-level feedback here by e-mail too.  Please feel free to submit
pull requests for eg. editorial improvements.

Once there's a bit more consensus on the API shape, I plan to write a
polyfill and W3C-style tests and then begin a prototype implementation in
Chromium.  We have some initial evidence to believe that this (in
partnership with a few key library authors) can make a substantial
improvement to the user experience on mobile.  I hope to be able to share
more concrete data on the real-world performance impact, but there's
obviously a chicken and egg problem here.

Thanks,
   Rick