We are about to release M57 which removes the rarely used webkitCancelRequestAnimationFrame.
https://developers.google.com/web/updates/2017/02/chrome-57-deprecations
https://www.chromestatus.com/feature/5588435494502400

Unfortunately, webkitCancelAnimationFrame and webkitRequestAnimationFrame are more widely used.
https://www.chromestatus.com/metrics/feature/timeline/popularity/304 0.01%
https://www.chromestatus.com/metrics/feature/timeline/popularity/14 0.03%

My understanding is that old but widely deployed versions of GWT use webkitRequestAnimationFrame, falling back to setTimeout if it are not available.

A proposed way forward is summarised in
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/3SZWAFN5uEY/s-RP_il6CAAJ

We would alias instead of having distinct implementations.

Unfortunately, webkitRequestAnimationFrame and requestAnimationFrame callbacks receive a slightly different timing argument.

We understand that Edge simply aliases webkitRequestAnimationFrame to requestAnimationFrame. Similar for webkitCancelAnimationFrame, so we suspect the timing argument issue will not actually be a problem.

An Intent will need to be written and posted to blink-dev.

This launch bug has not been modified in the last 90 days and has no milestone label. Please take a look and add appropriate milestone label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Downgrading to a regular bug. If prioritized, should be turned into a Launch-OWP bug.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot