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Legacy used Table as a sticky container for TD.

Bring TablesNG in sync with legacy, and make
table rows also use table as a sticky container.

Standard not settled yet, discussion at:
https://github.com/w3c/csswg-drafts/issues/5020

Makes 2 layout tests pass:

external/wpt/css/css-position/sticky/position-sticky-table-th-bottom.html
external/wpt/css/css-position/sticky/position-sticky-table-th-top.html

Makes 3 unit tests pass
LayoutBoxModelObjectTest.StickyPositionComplexTableNesting (layout_box_model_object_test.cc:886)
LayoutBoxModelObjectTest.StickyPositionNestedStickyTable (layout_box_model_object_test.cc:818)
LayoutBoxModelObjectTest.StickyPositionTableContainers (layout_box_model_object_test.cc:349)

Bug: 958381
Change-Id: If099efe32a6a23154b53bf96981f7176030cd52c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542737Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828994}