[TablesNG] NGTableBorders

Data structure that holds collapsed borders.

Bug: 958381
Change-Id: If9716b5c81f6869dfd07468677490546f1eed34e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2277060
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785966}

third_party/blink/renderer/core/layout/BUILD.gn

@@ -550,6 +550,8 @@ blink_core_sources("layout") {
     "ng/table/layout_ng_table_section.cc",
     "ng/table/layout_ng_table_section.h",
     "ng/table/layout_ng_table_section_interface.h",
+    "ng/table/ng_table_borders.cc",
+    "ng/table/ng_table_borders.h",
     "ng/table/ng_table_layout_algorithm_helpers.cc",
     "ng/table/ng_table_layout_algorithm_helpers.h",
     "ng/table/ng_table_layout_algorithm_types.cc",