Use rowgroup and columgroup properties to expose table headers.

Source/modules/accessibility/AXTableCell.h

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 40 matching lines @@
     // fills in the start location and column span of cell
     virtual void columnIndexRange(pair<unsigned, unsigned>& columnRange);
 
 protected:
     virtual AXObject* parentTable() const;
     int m_rowIndex;
     virtual AccessibilityRole determineAccessibilityRole() override final;
 
 private:
     bool isTableHeaderCell() const;
+    bool isRowHeaderCell() const;
+    bool isColumnHeaderCell() const;
+
     AccessibilityRole scanToDecideHeaderRole();
     // If a table cell is not exposed as a table cell, a TH element can serve as its title UI element.
     virtual AXObject* titleUIElement() const override final;
     virtual bool exposesTitleUIElement() const override final { return true; }
     virtual bool computeAccessibilityIsIgnored() const override final;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXTableCell, isTableCell());
 
 } // namespace blink
 
 #endif // AXTableCell_h