LibWeb: Properly handle thead and tfooter HTML tags

As the spec for the table fixup algorythm says:

> Treat table-row-groups in this spec also encompass the specialized
> table-header-groups and table-footer-groups.

Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp

@@ -210,7 +210,10 @@ static bool is_table_track(CSS::Display display)
 
 static bool is_table_track_group(CSS::Display display)
 {
- return display == CSS::Display::TableRowGroup || display == CSS::Display::TableColumnGroup;
+ // Unless explicitly mentioned otherwise, mentions of table-row-groups in this spec also encompass the specialized
+ // table-header-groups and table-footer-groups.
+ return display == CSS::Display::TableRowGroup || display == CSS::Display::TableHeaderGroup || display == CSS::Display::TableFooterGroup
+ || display == CSS::Display::TableColumnGroup;
 }
 
 static bool is_not_proper_table_child(const Node& node)
@@ -290,6 +293,18 @@ void TreeBuilder::generate_missing_child_wrappers(NodeWithStyle& root)
  wrap_in_anonymous<TableRowBox>(sequence, nearest_sibling);
  });
  });
+ // Unless explicitly mentioned otherwise, mentions of table-row-groups in this spec also encompass the specialized
+ // table-header-groups and table-footer-groups.
+ for_each_in_tree_with_display<CSS::Display::TableHeaderGroup>(root, [&](auto& parent) {
+ for_each_sequence_of_consecutive_children_matching(parent, is_not_table_row, [&](auto& sequence, auto nearest_sibling) {
+ wrap_in_anonymous<TableRowBox>(sequence, nearest_sibling);
+ });
+ });
+ for_each_in_tree_with_display<CSS::Display::TableFooterGroup>(root, [&](auto& parent) {
+ for_each_sequence_of_consecutive_children_matching(parent, is_not_table_row, [&](auto& sequence, auto nearest_sibling) {
+ wrap_in_anonymous<TableRowBox>(sequence, nearest_sibling);
+ });
+ });
 
  // An anonymous table-cell box must be generated around each sequence of consecutive children of a table-row box which are not table-cell boxes. !Testcase
  for_each_in_tree_with_display<CSS::Display::TableRow>(root, [&](auto& parent) {