Bug 1089718 - [music] Make the metadata parser sane

This seems like an inefficient way to do it. Can you pull the blob out of the L2 cache instead of using XHR on the URL? I gather that the point of getCoverBlob() is for IAC for the remote controls. And in that case having a file-backed blob is probably more efficient than creating a memory-backed blob with XHR.

I suppose you might need a special case to handle the placeholder album covers...