…apped bounds. r=kvark

When we calculate the repeating tile size, errors can be introduced,
such that there are cases it should be the same as the bounds, but is
slightly different. This can cause a new repetition where we did not
expect one. This patch makes the comparison when may force the tile size
to be the same as the snapped bounds more fuzzy.

Differential Revision: https://phabricator.services.mozilla.com/D67620

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/93cf130f59f97acc6ebb84c3505880cdcaca36c0