[LayoutNG] Refactor NGOutOfFlowLayoutPart member variables

NGOutOfFlowLayoutPart used to have a single containing block,
and it was defined by a NGOOFLP member variables.

With inline containing blocks, we have multiple containing blocks,
defined by ContainingBlockInfo.

This CL moves definition of default containing block out of multiple
member variables into single ContainingBlockInfo.

Bug: 635619
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I69dd499cb69c7e6fc56971e85882cd7e6241f99c
Reviewed-on: https://chromium-review.googlesource.com/829888
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524455}
2 files changed