Reduce forward declarations in core/rendering

Source/core/rendering/RenderButton.h

 /*
  * Copyright (C) 2005 Apple Computer
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #ifndef RenderButton_h
 #define RenderButton_h
 
 #include "core/html/HTMLInputElement.h"
 #include "core/rendering/RenderFlexibleBox.h"
 
 namespace WebCore {
 
-class RenderTextFragment;
-
 // RenderButtons are just like normal flexboxes except that they will generate an anonymous block child.
 // For inputs, they will also generate an anonymous RenderText and keep its style and content up
 // to date as the button changes.
 class RenderButton FINAL : public RenderFlexibleBox {
 public:
     explicit RenderButton(Element*);
     virtual ~RenderButton();
 
     virtual const char* renderName() const OVERRIDE { return "RenderButton"; }
     virtual bool isRenderButton() const OVERRIDE { return true; }
@@ skipping 24 matching lines @@
     virtual bool hasLineIfEmpty() const OVERRIDE { return isHTMLInputElement(node()); }
 
     RenderBlock* m_inner;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderButton, isRenderButton());
 
 } // namespace WebCore
 
 #endif // RenderButton_h