Implement "auto -> angle" animation on <marker> orient attribute.

Source/core/svg/SVGAngle.h

Index: Source/core/svg/SVGAngle.h
diff --git a/Source/core/svg/SVGAngle.h b/Source/core/svg/SVGAngle.h
index 2527847db514d0da939a513cac6c0a0299039f4b..d935d0868972916b7675bf84f94832a9f141827d 100644
--- a/Source/core/svg/SVGAngle.h
+++ b/Source/core/svg/SVGAngle.h
@@ -93,6 +93,7 @@ public:
     void convertToSpecifiedUnits(SVGAngleType unitType, ExceptionState&);
 
     SVGEnumeration<SVGMarkerOrientType>* orientType() { return m_orientType.get(); }
+    const SVGEnumeration<SVGMarkerOrientType>* orientType() const { return m_orientType.get(); }
     void orientTypeChanged();
 
     // SVGPropertyBase:
@@ -112,6 +113,8 @@ private:
     SVGAngle();
     SVGAngle(SVGAngleType, float, SVGMarkerOrientType);
 
+    void assign(const SVGAngle&);
+
     SVGAngleType m_unitType;
     float m_valueInSpecifiedUnits;
     RefPtr<SVGMarkerOrientEnumeration> m_orientType;