Issue #28003: Implement PEP 525 -- Asynchronous Generators.
diff --git a/Lib/asyncio/events.py b/Lib/asyncio/events.py
index c48c5be..cc9a986 100644
--- a/Lib/asyncio/events.py
+++ b/Lib/asyncio/events.py
@@ -248,6 +248,10 @@
         """
         raise NotImplementedError
 
+    def shutdown_asyncgens(self):
+        """Shutdown all active asynchronous generators."""
+        raise NotImplementedError
+
     # Methods scheduling callbacks.  All these return Handles.
 
     def _timer_handle_cancelled(self, handle):