Make typedefs lazy again

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index 31400493aad53d6698c6cd828f6d15dabe0d7a0f..9c4bf292abbfeaacfd7358bd893ad7b58acb9dfa 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -282,13 +282,11 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     var type = element.type;
     var name = element.name;
 
-    _loader.startTopLevel(element);
-    var fnType = js.statement('let # = dart.typedef(#, #);', [
+    var fnType = js.statement('let # = dart.typedef(#, () => #);', [
       name,
       js.string(name, "'"),
       _emitTypeName(type, lowerTypedef: true)
     ]);
-    _loader.finishTopLevel(element);
 
     return _finishClassDef(type, fnType);
   }