Fix identity and SVGAnimatedString issues with element_classes_test

sdk/lib/svg/dart2js/svg_dart2js.dart

 /**
  * Scalable Vector Graphics:
  * Two-dimensional vector graphics with support for events and animation.
  *
  * For details about the features and syntax of SVG, a W3C standard,
  * refer to the
  * [Scalable Vector Graphics Specification](http://www.w3.org/TR/SVG/).
  */
 library dart.dom.svg;
 
@@ skipping 4868 matching lines @@
 
   /**
    * Checks to see if the SVG element type is supported by the current platform.
    *
    * The tag should be a valid SVG element tag name.
    */
   static bool isTagSupported(String tag) {
     var e = new SvgElement.tag(tag);
     return e is SvgElement && !(e is UnknownElement);
   }
+
   // To suppress missing implicit constructor warnings.
   factory SvgElement._() { throw new UnsupportedError("Not supported"); }
 
   @DomName('SVGElement.abortEvent')
   @DocsEditable()
   @Experimental() // untriaged
   static const EventStreamProvider<Event> abortEvent = const EventStreamProvider<Event>('abort');
 
   @DomName('SVGElement.blurEvent')
   @DocsEditable()
@@ skipping 1899 matching lines @@
   @DomName('SVGVKernElement.SVGVKernElement')
   @DocsEditable()
   factory _SVGVKernElement() => _SvgElementFactoryProvider.createSvgElement_tag("vkern");
   /**
    * Constructor instantiated by the DOM when a custom element has been created.
    *
    * This can only be called by subclasses from their created constructor.
    */
   _SVGVKernElement.created() : super.created();
 }