Update object.dart and some comments.

lib/runtime/dart_sdk.js

Index: lib/runtime/dart_sdk.js
diff --git a/lib/runtime/dart_sdk.js b/lib/runtime/dart_sdk.js
index f92bcc5ce498e66b888b2ac14b2fa8eda13313a2..1c82925cffe8a2f0511d23a42432d25223bf3235 100644
--- a/lib/runtime/dart_sdk.js
+++ b/lib/runtime/dart_sdk.js
@@ -28177,7 +28177,7 @@ dart_library.library('dart_sdk', null, /* Imports */[
     constructors: () => ({new: [core.RegExp, [core.String], {multiLine: core.bool, caseSensitive: core.bool}]})
   });
   core.Set$ = dart.generic(E => {
-    class Set extends collection.IterableBase$(E) {
+    class Set extends core.Iterable$(E) {
       static new() {
         return collection.LinkedHashSet$(E).new();
       }