[LayoutNG] Removes per-child state from NGBlockLayoutAlgorithm.
Removes curr_bfc_offset_, curr_child_margins_, curr_margin_strut_ in
favour of stack variables.
This clears up the information flow between children, and makes it clear
*which* margin strut, etc is being used for a particular child's
positioning. (E.g. the OOFPositioned child's positioning was difficult
to determine before).
This introduces one regression which I'll investigate separately (static
position is weird with abs-pos legacy children now) - so I've removed the
LayoutNG CQ bot.
BUG=635619
Review-Url: https://codereview.chromium.org/2899413002
Cr-Commit-Position: refs/heads/master@{#476354}
4 files changed
