Updated SVGListPropertyHelper as per SVG2 Spec

Source/core/svg/SVGPathSegListTearOff.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 30 matching lines @@
 class ListItemPropertyTraits<SVGPathSeg> {
 public:
     typedef SVGPathSeg ItemPropertyType;
     // FIXME: Currently SVGPathSegitself is a tear-off.
     typedef SVGPathSeg ItemTearOffType;
 
     static PassRefPtrWillBeRawPtr<ItemPropertyType> getValueForInsertionFromTearOff(PassRefPtrWillBeRawPtr<ItemTearOffType> passNewItem, SVGElement* contextElement, const QualifiedName& attributeName)
     {
         ASSERT(attributeName == SVGNames::dAttr);
         RefPtrWillBeRawPtr<ItemTearOffType> newItem = passNewItem;
+
+        // Spec: If newItem is already in a list, then a new SVGPathSeg object is created with the same values as newItem and this item is inserted into the list.
+        // Otherwise, newItem itself is inserted into the list.
+        // https://svgwg.org/svg2-draft/paths.html#InterfaceSVGPathSegList
+        if (newItem->ownerList())
+            newItem = newItem->clone();
+
         newItem->setContextElement(contextElement);
         return newItem.release();
     }
 
     static PassRefPtrWillBeRawPtr<ItemTearOffType> createTearOff(PassRefPtrWillBeRawPtr<ItemPropertyType> passValue, SVGElement* contextElement, PropertyIsAnimValType, const QualifiedName&)
     {
         RefPtrWillBeRawPtr<SVGPathSeg> value = passValue;
         value->setContextElement(contextElement);
         return value.release();
     }
@@ skipping 10 matching lines @@
     }
 
 private:
     SVGPathSegListTearOff(PassRefPtrWillBeRawPtr<SVGPathSegList> target, SVGElement* contextElement, PropertyIsAnimValType propertyIsAnimVal, const QualifiedName& attributeName = QualifiedName::null())
         : SVGListPropertyTearOffHelper<SVGPathSegListTearOff, SVGPathSegList>(target, contextElement, propertyIsAnimVal, attributeName) { }
 };
 
 } // namespace blink
 
 #endif // SVGPathSegListTearOff_h