We should implement the proposed WPT behavior for <link rel=>:
https://github.com/web-platform-tests/rfcs/blob/master/rfcs/reftest_simplification.md

Specifically:
> In general, we shall make every file with at least one <link rel=match>/<link rel=mismatch> into a test; this will introduce new tests for all current references which currently chain onto further references.
> Further, it is proposed that we change the combinatorial behaviour to the one originally defined by the CSS WG: if there is at least one <link rel=match>, at least one must pass, and all <link rel=mismatch> must pass.