Allow determining if an SVG value has been specified

Source/core/svg/properties/NewSVGAnimatedProperty.h

Index: Source/core/svg/properties/NewSVGAnimatedProperty.h
diff --git a/Source/core/svg/properties/NewSVGAnimatedProperty.h b/Source/core/svg/properties/NewSVGAnimatedProperty.h
index 75774001cd68ef768d53569e874b485b4b9a849d..6d097c9d48a665340d7d04b00d87329ab21dc03c 100644
--- a/Source/core/svg/properties/NewSVGAnimatedProperty.h
+++ b/Source/core/svg/properties/NewSVGAnimatedProperty.h
@@ -67,7 +67,7 @@ public:
         return m_type;
     }
 
-    SVGElement* contextElement()
+    SVGElement* contextElement() const
     {
         return m_contextElement;
     }
@@ -92,6 +92,8 @@ public:
         m_isReadOnly = true;
     }
 
+    bool isSpecified() const;
+
 protected:
     NewSVGAnimatedPropertyBase(AnimatedPropertyType, SVGElement*, const QualifiedName& attributeName);
     void commitChange();