Import display: contents tests from csswg-test.

This were reviewed upstream in https://github.com/w3c/csswg-test/pull/1155

This should reduce the noise in https://codereview.chromium.org/2450093005, and
make it more manageable and straight-forward to review.

BUG=657748

Review-Url: https://codereview.chromium.org/2588093003
Cr-Commit-Position: refs/heads/master@{#439805}
62 files changed