Remove the generics from _FrozenElementList: causes checked mode failures

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index e10c1b6a673643f2dac56a61ce5f9f0bba41f657..4fe29f7b9f574adcec0f0f54e4eb26fe2f7b7808 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -13136,8 +13136,8 @@ 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;
 
   var dartClass_instance;