Add FetchNext to ShmEventLoop

I need this as a stop-gap until watchers work in simulation so that I
can receive every camera frame without using watchers.

Change-Id: Ic2c87fc11e69952ff8028e1484f5b236afdae70e
diff --git a/aos/events/simulated-event-loop.cc b/aos/events/simulated-event-loop.cc
index a23b18c..5fe1bf5 100644
--- a/aos/events/simulated-event-loop.cc
+++ b/aos/events/simulated-event-loop.cc
@@ -2,6 +2,7 @@
 
 #include <algorithm>
 
+#include "aos/logging/logging.h"
 #include "aos/queue.h"
 
 namespace aos {
@@ -11,6 +12,11 @@
   explicit SimulatedFetcher(SimulatedQueue *queue) : queue_(queue) {}
   ~SimulatedFetcher() {}
 
+  bool FetchNext() override {
+    LOG(FATAL, "Simulated event loops do not support FetchNext.");
+    return false;
+  }
+
   bool Fetch() override {
     if (index_ == queue_->index()) return false;