XMLHttpRequest.responseBlob

There is some interest from application developers at Google in being able
to get a Blob corresponding to the response body of a XMLHttpRequest.

The use case is to improve the efficiency of getting a Blob from a binary
resource downloaded via XHR.

The alternative is to play games with character encodings so that
responseText can be used to fetch an image as a string, and then use
BlobBuilder to reconstruct the image file, again being careful with the
implicit character conversions.  All of this is very inefficient.

Is there any appetite for adding a responseBlob getter on XHR?

Regards,
-Darin