Revert "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 b3475c700610fe91fd802bfa75c7ee8819ef798d..2dfc42c11a15ebde80f8077c0f1d4c5aa59b4f66 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -13142,8 +13142,8 @@ 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
-    implements ElementList, NodeListWrapper {
+class _FrozenElementList extends ListBase<Element>
+    implements ElementList<Element>, NodeListWrapper {
   final List<Node> _nodeList;
 
   var dartClass_instance;