Add a simulated message bridge

This gives us multi-node simulations!

Change-Id: I10fa955653766a26e4d11471a6dae5b47ea5cd1c
diff --git a/aos/events/simulated_event_loop.cc b/aos/events/simulated_event_loop.cc
index 0d8a488..108a485 100644
--- a/aos/events/simulated_event_loop.cc
+++ b/aos/events/simulated_event_loop.cc
@@ -5,6 +5,7 @@
 #include <string_view>
 
 #include "absl/container/btree_map.h"
+#include "aos/events/simulated_network_bridge.h"
 #include "aos/json_to_flatbuffer.h"
 #include "aos/util/phased_loop.h"
 
@@ -744,6 +745,10 @@
     node_factories_.emplace_back(
         new NodeEventLoopFactory(&scheduler_, this, node, &raw_event_loops_));
   }
+
+  if (configuration::MultiNode(configuration)) {
+    bridge_ = std::make_unique<message_bridge::SimulatedMessageBridge>(this);
+  }
 }
 
 SimulatedEventLoopFactory::~SimulatedEventLoopFactory() {}