Clean up forward declarations in Source/core/accessibility

Source/core/accessibility/AXARIAGrid.h

 /*
  * Copyright (C) 2009 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 16 matching lines @@
  */
 
 #ifndef AXARIAGrid_h
 #define AXARIAGrid_h
 
 #include "core/accessibility/AXTable.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 
-class AXTableCell;
-class AXTableHeaderContainer;
-
 class AXARIAGrid final : public AXTable {
-
 private:
     explicit AXARIAGrid(RenderObject*);
 public:
     static PassRefPtr<AXARIAGrid> create(RenderObject*);
     virtual ~AXARIAGrid();
 
     virtual bool isAriaTable() const override { return true; }
 
     virtual void addChildren() override;
 
 private:
     // ARIA treegrids and grids support selected rows.
     virtual bool supportsSelectedRows() override { return true; }
     virtual bool isMultiSelectable() const override { return true; }
     virtual bool isTableExposableThroughAccessibility() const override { return true; }
 
     bool addTableCellChild(AXObject*, HashSet<AXObject*>& appendedRows, unsigned& columnCount);
 };
 
 } // namespace blink
 
 #endif // AXARIAGrid_h