Make sure that classes in dart:html do not implement both List and List<E>.

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

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index 3bc56ef690f1d0e8c6ffd7c639a27bd4bad6353c..e04ec31010223c88ecb96000ba283ba629af0da9 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -259,7 +259,7 @@ $!STREAM_GETTER_SIGNATURES
 // ElementList as there are valid cases where a NodeList JavaScript object
 // contains Node objects that are not Elements.
 class _FrozenElementList<T extends Element> extends ListBase<T>
-    implements ElementList, NodeListWrapper {
+    implements ElementList<T>, NodeListWrapper {
   final List<Node> _nodeList;
   // The subset of _nodeList that are Elements.
   List<Element> _elementList;