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 8d1e2a8f714440c3e26b07f0bf6c02fe19ab4fab..1959d7f1f1e5d5808a993abbfa03c9499b60dba2 100644
--- a/lib/runtime/dart_sdk.js
+++ b/lib/runtime/dart_sdk.js
@@ -925,10 +925,11 @@ dart_library.library('dart_sdk', null, /* Imports */[
   };
   dart.setBaseClass = function(derived, base) {
     derived.prototype.__proto__ = base.prototype;
+    derived.__proto__ = base;
   };
   dart.setExtensionBaseClass = function(derived, base) {
     derived.prototype[dart._extensionType] = derived;
-    dart.setBaseClass(derived, base);
+    derived.prototype.__proto__ = base.prototype;
   };
   dart.throwCastError = function(object, actual, type) {
     dart.throw(new _js_helper.CastErrorImplementation(object, dart.typeName(actual), dart.typeName(type)));