Image fetching does not respect crossOrigin attribute

[jdm]

Step 18 of https://html.spec.whatwg.org/multipage/images.html#updating-the-image-data and step 14 of https://html.spec.whatwg.org/multipage/images.html#reacting-to-environment-changes use https://html.spec.whatwg.org/multipage/urls-and-fetching.html#create-a-potential-cors-request to create a request with certain properties based on the state of the image element's crossorigin attribute. Our implementation does not follow these steps correctly.