Don't cache SVG CssClassSet

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

Index: tools/dom/templates/html/impl/impl_SVGElement.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_SVGElement.darttemplate b/tools/dom/templates/html/impl/impl_SVGElement.darttemplate
index 1d9f06e3ad7b78461c6853493a53f1d593120113..dd235bc685f4538c59642fdc8496aea1294007fb 100644
--- a/tools/dom/templates/html/impl/impl_SVGElement.darttemplate
+++ b/tools/dom/templates/html/impl/impl_SVGElement.darttemplate
@@ -54,13 +54,7 @@ $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS
     return fragment.nodes.where((e) => e is SvgElement).single;
   }
 
-  _AttributeClassSet _cssClassSet;
-  CssClassSet get classes {
-    if (_cssClassSet == null) {
-      _cssClassSet = new _AttributeClassSet(this);
-    }
-    return _cssClassSet;
-  }
+  CssClassSet get classes => new _AttributeClassSet(this);
 
   List<Element> get children => new FilteredElementList<Element>(this);