Remove frame flattening support as Chromium has no intention of using it

Source/core/rendering/RenderFrame.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Simon Hausmann <hausmann@kde.org>
  *           (C) 2000 Stefan Schimanski (1Stein@gmx.de)
  * Copyright (C) 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  *
  * 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.
@@ skipping 13 matching lines @@
 #include "config.h"
 #include "RenderFrame.h"
 
 #include "FrameView.h"
 #include "HTMLFrameElement.h"
 #include "RenderView.h"
 
 namespace WebCore {
 
 RenderFrame::RenderFrame(HTMLFrameElement* frame)
-    : RenderFrameBase(frame)
+    : RenderPart(frame)
 {
     setInline(false);
 }
 
 FrameEdgeInfo RenderFrame::edgeInfo() const
 {
     HTMLFrameElement* element = static_cast<HTMLFrameElement*>(node());
     return FrameEdgeInfo(element->noResize(), element->hasFrameBorder());
 }
 
@@ skipping 14 matching lines @@
     int marginWidth = element->marginWidth();
     int marginHeight = element->marginHeight();
 
     if (marginWidth != -1)
         view->setMarginWidth(marginWidth);
     if (marginHeight != -1)
         view->setMarginHeight(marginHeight);
 }
 
 } // namespace WebCore