Migrate css_selector_test off unittest.
Migrate css_selector_test off unittest.

This test was actually totally broken. It called
useHtmlIndividualConfiguration(), which tells the test runner to treat
each group() as a separate test. But it had no group() calls at all, so
the test runner didn't enqueue *anything* for it. It was completely
skipped. :-O

Change-Id: Ib7b030c94d286f467601ec490308c32fb500c7a8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137291
Commit-Queue: Bob Nystrom <afede3a9ebedb865bee78398feff6fbe97068f17@google.com>
Commit-Queue: Srujan Gaddam <4175f2f2dd3cde6c8ffb10fc9674dc09abf813fe@google.com>
Auto-Submit: Bob Nystrom <afede3a9ebedb865bee78398feff6fbe97068f17@google.com>
Reviewed-by: Srujan Gaddam <4175f2f2dd3cde6c8ffb10fc9674dc09abf813fe@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk