[LayoutNG] Part 3 of 3: Move NGFragBuilder::AddOOFChildCandidate to NGContainerFragmentBuilder

Also move GetAndClearOutOfFlowDescendantCandidates

This is the last part of the 3 part refactor.

Bug: 740993
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I834f393e76a83d5860e1fa9445bde755a33a9507
Reviewed-on: https://chromium-review.googlesource.com/736901
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512031}
4 files changed