[mojo-edk] Revert ObserveProxy retransmission behavior

mojo/edk/system/node_controller.h

Index: mojo/edk/system/node_controller.h
diff --git a/mojo/edk/system/node_controller.h b/mojo/edk/system/node_controller.h
index 11d5f196c335106d9cdef3e7a376d748134a2f14..2cdcd90253a200336ec8f1162ba7de52bf9af7ec 100644
--- a/mojo/edk/system/node_controller.h
+++ b/mojo/edk/system/node_controller.h
@@ -286,6 +286,8 @@ class NodeController : public ports::NodeDelegate,
   // Ensures that there is only one incoming messages task posted to the IO
   // thread.
   bool incoming_messages_task_posted_ = false;
+  // Flag to fast-path checking |incoming_messages_|.
+  AtomicFlag incoming_messages_flag_;
 
   // Guards |shutdown_callback_|.
   base::Lock shutdown_lock_;