[CSS] Fix test for css invalidation so that it fails without ::part.

The test was testing that the element ended up green (starting red)
however, if the browser has no support at all for ::part then the
element actually starts green and stays green.



Bug: 805271
Change-Id: Ida40c7963aa3a00c3d197b1309ddaea49e4f3b92
Reviewed-on: https://chromium-review.googlesource.com/c/1369500
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Fergal Daly <fergal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615435}
1 file changed