The example code has a commit() inside a RAF. This is not a supported use case.

Perhaps we should add a warning then?

It shouldn't flicker regardless of use. It is not required to constantly render to a canvas so even if it's skipping frames because of incorrect use it should not flicker.

Here's a perfectly valid usecase

http://jsfiddle.net/greggman/y36aujrf/

It's trying to render at 15fps so it does this

  let then = -1000;
  function loop(time) {
    time *= 0.001;
    const elapsed = time - then;
    if (elapsed > 1 / 15) {
      then = time;
      render();
      gl.commit();
    }
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);

requestAnimationFrame() on a web worker has (or seems to have) the semantic that it automatically commits updates to the OffscreenCanvas contexts which are updated within its callback's scope, similarly to how the main thread's requestAnimationFrame works.

For this reason it's an error to call commit() from within a worker's requestAnimationFrame callback. The spec should be changed to make commit() throw an exception in this case. Some work is in progress on the specs in https://github.com/whatwg/html/pull/3677 and another pull request which I can't find immediately.

Here's an update of your resizing example which removes the incorrect call to commit() and works well:

http://jsfiddle.net/gmpkvu30/2/

and an update of your 15 FPS rendering example which removes the call to commit() and works well:

http://jsfiddle.net/y36aujrf/3/

Thanks for putting these together; we should change the spec and implementation so that they clearly show incorrect uses of the API and work well cross-browser.