1) the `crossOrigin='anonymous'` tells the browser to actually honour
CORS on the image
2) the dot is now always 1/5 of the icon, even for large icons
3) we use `toBlob` instead of `toDataURL` because
https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL
says so
4) the test now blinks the dot, so it tests the actual code
5) if there's a problem during the test, we log the error, so people
can tell it to us
Thanks to Ares on Discord for reporting the problems.
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