Support stopping and starting logging at runtime

Change-Id: If1e1b7119808d1f56e96efb71ea7000e0fa13fe8
diff --git a/aos/events/logging/uuid.h b/aos/events/logging/uuid.h
index b81b811..0387a4b 100644
--- a/aos/events/logging/uuid.h
+++ b/aos/events/logging/uuid.h
@@ -13,6 +13,8 @@
   // Returns a randomly generated UUID.  This is known as a UUID4.
   static UUID Random();
 
+  static UUID Zero();
+
   std::string_view string_view() const {
     return std::string_view(data_.data(), data_.size());
   }