[LayoutNG] Fix negative margins on inline boxes

This patch fixes computing size of inline boxes that have
negative inline margins.

It looks like we didn't have enough test coverage when
`NGFragmentGeometry` was introduced.

Bug: 971622
Change-Id: Icd0f5300ef76a873ec25b8d96756884da954d184
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1662249
Reviewed-by: Aleks Totic <atotic@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669699}
3 files changed