Intent to ship: OffscreenCanvas

[Andrew Osmond]

In release 105, I intend to turn OffscreenCanvas on by default on all platforms.

We have been shipping OffscreenCanvas as an origin trial for Zoom only since release 99 (see bug 1751721). The initial implementation only included full support for WebGL but we now included support for all of the context types (WebGL, 2D, BitmapRenderer, WebGPU [subject to WebGPU itself shipping]).

The final pieces for text rendering with 2D contexts were landed in 104, and we were able to turn it on for nightly and early beta users in 104 as well with minimal issue. This work includes exposing FontFaceSet on workers as user fonts are a dependency.

It has been developed behind the pref gfx.offscreencanvas.enabled and layout.css.font-loading-api.workers.enabled.

Chrome has been shipping OffscreenCanvas since Chrome 69 / 2018-09-03. Safari has yet to ship.

Bug to turn on by default in release:
https://bugzilla.mozilla.org/show_bug.cgi?id=1779009

Standards:
https://html.spec.whatwg.org/multipage/canvas.html#the-offscreencanvas-interface
https://drafts.csswg.org/css-font-loading