add tests for <img crossorigin> / img.crossOrigin

[sideshowbarker]

No description provided.

[foolip]

Spec is https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element

3 years later, looks like this is still missing. semantics/embedded-content/the-img-element/relevant-mutations.html does involve the attribute, but it a tangential way, and I can't find any others, just a bunch of tests for the script element with the crossorigin attribute.

[xiuqijix]

@foolip, seems these two files redirect-to-url-with-credentials.https.html and image-loads.html have tested it.

[foolip]

Thanks @kaixinjxq, you're right. Those tests came from #8976 and #11171, so thanks @youennf!