interop: blob with empty content type is not converted to text/xml

[dlrobertson]

According to https://xhr.spec.whatwg.org/#response-mime-type:

If mimeType is failure, then set mimeType to text/xml.

Note: The content-type of the blob is set to "" (an invalid mime type) when the input type is not set or is invalid.

Test	Firefox	Chrome	Safari
no content type	text/xml	null	""
bad content type	text/xml	null	""

Related to: whatwg/fetch#1464 and whatwg/fetch#1436

[annevk]

I'm not entirely sure how to interpret this. Are you simultaneously pointing out that it's inconsistent with blobs and that browsers are not aligned on this?

[dlrobertson]

Ah, sorry just that browsers are not aligned on this.

[annevk]

I see, I kinda suspect this already has test coverage so unless that's not the case or someone wants to make a change to the spec this might be a good fit for the Interop effort?