allow JS builtin to be typed as needed

lib/runtime/dart/html.js

Index: lib/runtime/dart/html.js
diff --git a/lib/runtime/dart/html.js b/lib/runtime/dart/html.js
index 3889a09e134d3a22df4471a9076daeaf328a6726..2694494cdf1ef7c6ee607fc6b4b43f7c56b5f78e 100644
--- a/lib/runtime/dart/html.js
+++ b/lib/runtime/dart/html.js
@@ -10065,13 +10065,13 @@ dart_library.library('dart/html', null, /* Imports */[
           return dart.as(wrap_jso(e.raw.classList), DomTokenList);
         }
         static _classListLength(list) {
-          return dart.as(list.raw.length, core.int);
+          return list.raw.length;
         }
         static _classListContains(list, value) {
-          return dart.as(list.raw.contains(value), core.bool);
+          return list.raw.contains(value);
         }
         static _classListContainsBeforeAddOrRemove(list, value) {
-          return dart.as(list.raw.contains(value), core.bool);
+          return list.raw.contains(value);
         }
         static _classListAdd(list, value) {
           list.raw.add(value);