Fix identity and SVGAnimatedString issues with element_classes_test

tools/dom/templates/html/impl/impl_SVGElement.darttemplate

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 class _AttributeClassSet extends CssClassSetImpl {
   final Element _element;
 
   _AttributeClassSet(this._element);
@@ skipping 125 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 $CLASSNAME.tag(tag);
     return e is $CLASSNAME && !(e is UnknownElement);
   }
+
+$if JSINTEROP
+  String get className => _svgClassName.baseVal;
+
+  // Unbelievable hack. We can't create an SvgAnimatedString, but we can get
+  // the existing one and change its baseVal.
+  // TODO(alanknight): Handle suppressing the SVGAnimated<*> better
+  set className(String s) {
+    var oldClass = _svgClassName;
+    oldClass.baseVal = s;
+    super.className = oldClass;
+  }
+$endif

[terry, 2015/08/17 14:40:29]

Is it a bug that we can't create an SvgAnimatedString?  There is a create method
but the IDL doesn't expose that should we be able to construct an
SvgAnimatedString by allowing a constructor to call create?

 $!MEMBERS
 }