Use effective columns when cells with colspan are present.

Source/modules/accessibility/AXTableColumn.cpp

Index: Source/modules/accessibility/AXTableColumn.cpp
diff --git a/Source/modules/accessibility/AXTableColumn.cpp b/Source/modules/accessibility/AXTableColumn.cpp
index 556b19919c7dc4cba15e26d1a08e76979f028084..8a228e589d2a1e254f94a356310d0372d096b61c 100644
--- a/Source/modules/accessibility/AXTableColumn.cpp
+++ b/Source/modules/accessibility/AXTableColumn.cpp
@@ -101,9 +101,9 @@ void AXTableColumn::headerObjectsForColumn(AccessibilityChildrenVector& headers)
             if (!layoutCell)
                 continue;
 
-            // Whenever cell's col is less then current column index, we've found the cell with colspan.
+            // Whenever cell's effective col is less then current column index, we've found the cell with colspan.
             // We do not need to add this cell, it's already been added.
-            if (layoutCell->col() < m_columnIndex)
+            if (layoutCell->table()->colToEffCol(layoutCell->col()) < m_columnIndex)
                 continue;
 
             AXObject* cell = axObjectCache()->getOrCreate(layoutCell->node());