Remove the generics from _FrozenElementList: causes checked mode failures

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index cfc823fc011bbcefb1f2ee4ab2103bbe90369519..12508836d1b0cc2e947c30e4e150a8e74b6803c8 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -12447,8 +12447,8 @@ abstract class ElementList<T extends Element> extends ListBase<T> {
 // declared to return `ElementList`.  This provides all the static analysis
 // benefit so there is no need for this class have a constrained type parameter.
 //
-class _FrozenElementList extends ListBase<Element>
-    implements ElementList<Element>, NodeListWrapper {
+class _FrozenElementList extends ListBase
+    implements ElementList, NodeListWrapper {
   final List<Node> _nodeList;
 
   _FrozenElementList._wrap(this._nodeList);