Add tests for SVG sizing inside <object>

Sizing of SVGs inside <object> is lacking interoperability. Add test with current specification interpretation to see where we stand. HTML, CSS 2.1 and SVG all involved to some degree here, but the basic principles comes from CSS 2.1, Visual formatting model details.

I haven't added much documentation to the code, erring on the side of being terse rather than verbose. If you think more explanations are necessary, I'll gladly add them. Since this is my first pull request to web-platform-tests I welcome all sorts of feedback.

Test scores:

Firefox: 648/648
Chrome: 540/648
IE10: 490/648
(Opera Presto: 648/648)