Change I5a3cdeb7d53485f161ccf8133e76850cdf5b4579 introduced tests
for existence of all local files referenced in CSS. It's currently
failing changes even when the referenced files have been commented
out. This change ensures that commented-out files are not included
in the testing list.
Change-Id: I2ad74c13a9cf36e96a7d7451bf229856bcd18422
