[TablesNG] Fix empty section border spacing

Borders spacing for empty border sections was not being
handled correctly. Failing tests included:

external/wpt/css/css-tables/bounding-box-computation-3.html
fast/table/anonymous-table-section-removed.html
fast/table/multiple-captions-display.xhtml

The correct behaviour is:
- empty sections do contribute to border spacing
- sections are empty if they have no children. This is non-intuitive:
abspos child, or an empty row still make section non-empty. This
matches empty criteria for table cell when computing baseline.

Bug: 958381
Change-Id: Ib960a54794897ef346bfc26821efe26fb33a853f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2578696
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834884}

third_party/blink/renderer/core/layout/ng/ng_box_fragment.h

@@ -68,10 +68,10 @@ class CORE_EXPORT NGBoxFragment final : public NGFragment {
     return physical_box_fragment.Padding().ConvertToLogical(writing_direction_);
   }
 
-  bool HasDescendantsForTableCell() const {
+  bool HasDescendantsForTablePart() const {
     const NGPhysicalBoxFragment& box_fragment =
         To<NGPhysicalBoxFragment>(physical_fragment_);
-    DCHECK(box_fragment.IsTableNGCell());
+    DCHECK(physical_fragment_.IsTableNGPart() || box_fragment.IsTableNGCell());
     return !box_fragment.Children().empty() ||
            box_fragment.HasOutOfFlowPositionedFragmentainerDescendants() ||
            box_fragment.HasOutOfFlowPositionedDescendants();

third_party/blink/renderer/core/layout/ng/table/ng_table_layout_algorithm.cc

@@ -786,28 +786,29 @@ scoped_refptr<const NGLayoutResult> NGTableLayoutAlgorithm::GenerateFragment(
 
   base::Optional<LayoutUnit> table_baseline;
   wtf_size_t section_index = 0;
-  bool has_section = false;
+  bool needs_end_border_spacing = false;
   for (NGBlockNode section : grouped_children) {
     scoped_refptr<const NGLayoutResult> section_result =
         section.Layout(CreateSectionConstraintSpace(section_index++));
     const NGPhysicalBoxFragment& physical_fragment =
         To<NGPhysicalBoxFragment>(section_result->PhysicalFragment());
     NGBoxFragment fragment(table_writing_direction, physical_fragment);
-    if (fragment.BlockSize() != LayoutUnit() || !has_section)
+    if (fragment.HasDescendantsForTablePart()) {
       section_offset.block_offset += border_spacing.block_size;
+      needs_end_border_spacing = true;
+    }
     container_builder_.AddResult(*section_result, section_offset);
     if (!table_baseline) {
       if (const auto& section_baseline = fragment.Baseline())
         table_baseline = *section_baseline + section_offset.block_offset;
     }
     section_offset.block_offset += fragment.BlockSize();
-    has_section = true;
   }
-  if (has_section)
+  if (needs_end_border_spacing)
     section_offset.block_offset += border_spacing.block_size;
   LayoutUnit column_block_size =
       section_offset.block_offset - border_padding.block_start;
-  if (has_section)
+  if (needs_end_border_spacing)
     column_block_size -= border_spacing.block_size * 2;
 
   const LayoutUnit grid_block_size = std::max(

third_party/blink/renderer/core/layout/ng/table/ng_table_layout_algorithm_utils.cc

@@ -571,7 +571,7 @@ void NGRowBaselineTabulator::ProcessCell(
     const bool is_parallel,
     const bool descendant_depends_on_percentage_block_size) {
   if (is_parallel && is_baseline_aligned &&
-      fragment.HasDescendantsForTableCell()) {
+      fragment.HasDescendantsForTablePart()) {
     max_cell_baseline_depends_on_percentage_block_descendant_ |=
         descendant_depends_on_percentage_block_size;
     const LayoutUnit cell_baseline = fragment.FirstBaselineOrSynthesize();