Implement no-arg watchers efficiently in ShmEventLoop

Change-Id: I0efd8d3a639a1c6bb959b2ec263ffe8a3a84917d
diff --git a/aos/events/shm_event_loop.h b/aos/events/shm_event_loop.h
index fa870b8..d3f1295 100644
--- a/aos/events/shm_event_loop.h
+++ b/aos/events/shm_event_loop.h
@@ -52,6 +52,9 @@
       const Channel *channel,
       std::function<void(const Context &context, const void *message)> watcher)
       override;
+  void MakeRawNoArgWatcher(
+      const Channel *channel,
+      std::function<void(const Context &context)> watcher) override;
 
   TimerHandler *AddTimer(std::function<void()> callback) override;
   aos::PhasedLoopHandler *AddPhasedLoop(