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

Source/core/rendering/svg/RenderSVGText.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * Copyright (C) 2006 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) 2006 Oliver Hunt <ojh16@student.canterbury.ac.nz>
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 2010-2012. All rights reserved.
  * Copyright (C) 2012 Google Inc.
  *
@@ skipping 450 matching lines @@
     ASSERT_NOT_REACHED();
     return false;
 }
 
 PositionWithAffinity RenderSVGText::positionForPoint(const LayoutPoint& pointInContents)
 {
     RootInlineBox* rootBox = firstRootBox();
     if (!rootBox)
         return createPositionWithAffinity(0, DOWNSTREAM);
 
-    ASSERT_WITH_SECURITY_IMPLICATION(rootBox->isSVGRootInlineBox());
     ASSERT(!rootBox->nextRootBox());
     ASSERT(childrenInline());
 
-    InlineBox* closestBox = static_cast<SVGRootInlineBox*>(rootBox)->closestLeafChildForPosition(pointInContents);
+    InlineBox* closestBox = toSVGRootInlineBox(rootBox)->closestLeafChildForPosition(pointInContents);
     if (!closestBox)
         return createPositionWithAffinity(0, DOWNSTREAM);
 
     return closestBox->renderer()->positionForPoint(LayoutPoint(pointInContents.x(), closestBox->y()));
 }
 
 void RenderSVGText::absoluteQuads(Vector<FloatQuad>& quads, bool* wasFixed) const
 {
     quads.append(localToAbsoluteQuad(strokeBoundingBox(), 0 /* mode */, wasFixed));
 }
@@ skipping 65 matching lines @@
     return 0;
 }
 
 // Fix for <rdar://problem/8048875>. We should not render :first-letter CSS Style
 // in a SVG text element context.
 void RenderSVGText::updateFirstLetter()
 {
 }
 
 }