[LayoutNG] Support rewinding unpositioned floats

This patch supports NGLineBreaker to rewind unpositioned
floats.

When rewinding floats occurs, LayoutNG either position them
incorrectly, or hit DCHECK in paint due to duplicated ID.
This patch fixes it for unpositioned foats by matching to
Edge and Gecko.

Blink considers such floats as if it were committed
(positioned in LayoutNG terminologies) and thus the position
is incorrect.

Bug: 636993
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I884879b2034d2f63ae248f70de3edeb27d71cafe
Reviewed-on: https://chromium-review.googlesource.com/1136262
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575357}
7 files changed