[LayoutNG] Fix first-line baseline when 'overflow' is not 'visible'

This patch fixes first-line baseline when the 'overflow'
property is other than 'visible'.

CSS2 states that:
  The baseline of an 'inline-block' is the baseline of its
  last line box in the normal flow, unless it has either no
  in-flow line boxes or if its 'overflow' property has a
  computed value other than 'visible', in which case the
  baseline is the bottom margin edge.
https://drafts.csswg.org/css2/visudet.html#propdef-vertical-align

This rule should apply only to 'inline-block', but it was
incorrectly applied to first-line baseline as well.

This patch fixes incorrect alignment in the comment lines of
Gerrit code review site.

Bug: 636993
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I49ffd8c050f384765c61c5678a431fa74492356d
Reviewed-on: https://chromium-review.googlesource.com/1140336
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576294}
6 files changed