Use Length for the stroke-dashoffset property in SVGLayoutStyle

Source/core/layout/style/SVGLayoutStyleDefs.h

 /*
     Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
                   2004, 2005 Rob Buis <buis@kde.org>
     Copyright (C) Research In Motion Limited 2010. All rights reserved.
 
     Based on khtml code by:
     Copyright (C) 2000-2003 Lars Knoll (knoll@kde.org)
               (C) 2000 Antti Koivisto (koivisto@kde.org)
               (C) 2000-2003 Dirk Mueller (mueller@kde.org)
               (C) 2002-2003 Apple Computer, Inc.
@@ skipping 143 matching lines @@
     bool operator==(const StyleStrokeData&) const;
     bool operator!=(const StyleStrokeData& other) const
     {
         return !(*this == other);
     }
 
     float opacity;
     float miterLimit;
 
     RefPtrWillBePersistent<SVGLength> width;
-    RefPtrWillBePersistent<SVGLength> dashOffset;
+    Length dashOffset;
     RefPtrWillBePersistent<SVGLengthList> dashArray;
 
     SVGPaintType paintType;
     Color paintColor;
     String paintUri;
     SVGPaintType visitedLinkPaintType;
     Color visitedLinkPaintColor;
     String visitedLinkPaintUri;
 
 private:
@@ skipping 100 matching lines @@
         Length rx;
         Length ry;
     private:
         StyleLayoutData();
         StyleLayoutData(const StyleLayoutData&);
     };
 
 } // namespace blink
 
 #endif // SVGLayoutStyleDefs_h