Add toSVGRootInlineBox(), and use it as much as we can

Source/core/rendering/RenderBlockLineLayout.cpp

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google 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 1445 matching lines @@
     // Now position our text runs vertically.
     computeBlockDirectionPositionsForLine(lineBox, bidiRuns.firstRun(), textBoxDataMap, verticalPositionCache);
 
     // SVG text layout code computes vertical & horizontal positions on its own.
     // Note that we still need to execute computeVerticalPositionsForLine() as
     // it calls InlineTextBox::positionLineBox(), which tracks whether the box
     // contains reversed text or not. If we wouldn't do that editing and thus
     // text selection in RTL boxes would not work as expected.
     if (isSVGRootInlineBox) {
         ASSERT(isSVGText());
-        static_cast<SVGRootInlineBox*>(lineBox)->computePerCharacterLayoutInformation();
+        toSVGRootInlineBox(lineBox)->computePerCharacterLayoutInformation();
     }
 
     // Compute our overflow now.
     lineBox->computeOverflow(lineBox->lineTop(), lineBox->lineBottom(), textBoxDataMap);
 
     return lineBox;
 }
 
 // Like LayoutState for layout(), LineLayoutState keeps track of global information
 // during an entire linebox tree layout pass (aka layoutInlineChildren).
@@ skipping 2082 matching lines @@
     lineGridBox->alignBoxesInBlockDirection(logicalHeight(), textBoxDataMap, verticalPositionCache);
 
     setLineGridBox(lineGridBox);
 
     // FIXME: If any of the characteristics of the box change compared to the old one, then we need to do a deep dirtying
     // (similar to what happens when the page height changes). Ideally, though, we only do this if someone is actually snapping
     // to this grid.
 }
 
 }