Requires support for SVG backgrounds. Runs but fails in:
Test fails because implementations don't resize the image before applying background-position.
[Simon] I've looked into fixing this in WebKit <https://bugs.webkit.org/show_bug.cgi?id=47156>; it's do-able but not trivial.
[dbaron] Also see Gecko bug. I think we're not following one of the rules in the spec (see comment 8 in the bug).
[Simon] We expect to get 2 implementations (WebKit, Gecko?)