[LayoutNG] Fix non-nested multiple 'vertical-align: top/bottom'

Following the fix for nested case in r588042 (CL:1198887),
this patch fixes multiple but non-nested 'vertical-align:
top' and 'bottom' applied to one root line box.

In such case, it is required to compute the tallest box
within the line and align 'top' and 'bottom' boxes to the
tallest box.

Bug: 636993
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Ifea0cb7a24a85998f26f02fa0edd9ab7cf6edb9c
Reviewed-on: https://chromium-review.googlesource.com/1199386
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588637}
4 files changed