Remove some dead code from rendering/ folder

Source/core/rendering/RenderIFrame.cpp

 /*
  * Copyright (C) 2010 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 45 matching lines @@
     LayerType type = RenderPart::layerTypeRequired();
     if (type != NoLayer)
         return type;
 
     if (style()->resize() != RESIZE_NONE)
         return NormalLayer;
 
     return ForcedLayer;
 }
 
-RenderView* RenderIFrame::contentRootRenderer() const
-{
-    // FIXME: Is this always a valid cast? What about plugins?
-    ASSERT(!widget() || widget()->isFrameView());
-    FrameView* childFrameView = toFrameView(widget());
-    return childFrameView ? childFrameView->frame().contentRenderer() : 0;
-}
-
 void RenderIFrame::layout()
 {
     ASSERT(needsLayout());
 
     updateLogicalWidth();
     // No kids to layout as a replaced element.
     updateLogicalHeight();
 
     m_overflow.clear();
     addVisualEffectOverflow();
     updateLayerTransform();
 
     clearNeedsLayout();
 }
 
 }