[LayoutNG] Properly handle block-end borders.

We previously didn't correctly handle block-end borders.

This fixes a couple of subtle bugs:
 - We don't grow the block-size of a fragment if it doesn't have
   any content.
 - We expand to encapsulate floats first, then grow to encapsulate
   the border.

Bug: 	635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I7770a1d23a9c25fcab51e2e681e00e4b4d3e9d08
Reviewed-on: https://chromium-review.googlesource.com/770645
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517220}
2 files changed