[runtime] Fix effect of setting .prototype on generator functions.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 8461bef082ad6c5d17876e4210bdf63438c5d28e..b6e9c25d0f49d92eb382042c904a6f56d9d0b96d 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -749,6 +749,8 @@ void Genesis::CreateIteratorMaps(Handle<JSFunction> empty) {
       factory()->NewJSObject(isolate()->object_function(), TENURED);
   Handle<JSObject> generator_object_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);
+  native_context()->set_initial_generator_prototype(
+      *generator_object_prototype);
   SetObjectPrototype(generator_object_prototype, iterator_prototype);
   Handle<JSObject> generator_function_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);