Support stopping and starting logging at runtime

Change-Id: If1e1b7119808d1f56e96efb71ea7000e0fa13fe8
diff --git a/aos/events/logging/uuid.cc b/aos/events/logging/uuid.cc
index 9298c8b..376fa95 100644
--- a/aos/events/logging/uuid.cc
+++ b/aos/events/logging/uuid.cc
@@ -57,4 +57,10 @@
   return result;
 }
 
+UUID UUID::Zero() {
+  UUID result;
+  result.data_.fill(0);
+  return result;
+}
+
 }  // namespace aos