[es6] Class extends may not be a generator function

src/runtime/runtime-classes.cc

Index: src/runtime/runtime-classes.cc
diff --git a/src/runtime/runtime-classes.cc b/src/runtime/runtime-classes.cc
index 167abcc310642710c6bbe9fe57735e38c277189b..dafaacf06293fffa99fbb7a6c9354bfc6d2853ef 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -119,6 +119,12 @@ RUNTIME_FUNCTION(Runtime_DefineClass) {
     if (super_class->IsNull()) {
       prototype_parent = isolate->factory()->null_value();
     } else if (super_class->IsSpecFunction()) {
+      if (Handle<JSFunction>::cast(super_class)->shared()->is_generator()) {
+        Handle<Object> args[1] = {super_class};
+        THROW_NEW_ERROR_RETURN_FAILURE(
+            isolate,
+            NewTypeError("extends_value_generator", HandleVector(args, 1)));
+      }
       ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
           isolate, prototype_parent,
           Runtime::GetObjectProperty(isolate, super_class,