[SVG] SVGLength{,List} migration to new SVG property impl.

Source/core/rendering/svg/RenderSVGTextPath.cpp

 /*
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * 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
@@ skipping 38 matching lines @@
     // supplemental transformation relative to the current user coordinate system for
     // the current 'text' element, including any adjustments to the current user coordinate
     // system due to a possible transform attribute on the current 'text' element.
     // http://www.w3.org/TR/SVG/text.html#TextPathElement
     pathData.transform(pathElement->animatedLocalTransform());
     return pathData;
 }
 
 float RenderSVGTextPath::startOffset() const
 {
-    return toSVGTextPathElement(node())->startOffsetCurrentValue().valueAsPercentage();
+    return toSVGTextPathElement(node())->startOffset()->currentValue()->valueAsPercentage();
 }
 
 }