Use isTableHeaderCell() where appropriate.

Source/modules/accessibility/AXTableCell.cpp

 /*
  * 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 177 matching lines @@
 AXObject* AXTableCell::titleUIElement() const
 {
     // Try to find if the first cell in this row is a <th>. If it is,
     // then it can act as the title ui element. (This is only in the
     // case when the table is not appearing as an AXTable.)
     if (isTableCell() || !m_renderer || !m_renderer->isTableCell())
         return 0;
 
     // Table cells that are th cannot have title ui elements, since by definition
     // they are title ui elements
-    Node* node = m_renderer->node();
-    if (node && node->hasTagName(thTag))
+    if (isTableHeaderCell())
         return 0;
 
     RenderTableCell* renderCell = toRenderTableCell(m_renderer);
 
     // If this cell is in the first column, there is no need to continue.
     int col = renderCell->col();
     if (!col)
         return 0;
 
     int row = renderCell->rowIndex();
 
     RenderTableSection* section = renderCell->section();
     if (!section)
         return 0;
 
     RenderTableCell* headerCell = section->primaryCellAt(row, 0);
     if (!headerCell || headerCell == renderCell)
         return 0;
 
     Node* cellElement = headerCell->node();
     if (!cellElement || !cellElement->hasTagName(thTag))
         return 0;
 
     return axObjectCache()->getOrCreate(headerCell);
 }
 
 } // namespace blink