Network traffic annotation stored in url_request.

net/traffic_annotation/network_traffic_annotation.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_TRAFFIC_ANNOTATION_NETWORK_TRAFFIC_ANNOTATION_H_
 #define NET_TRAFFIC_ANNOTATION_NETWORK_TRAFFIC_ANNOTATION_H_
 
 namespace net {
 
 // Defined type for network traffic annotation tags.
@@ skipping 19 matching lines @@
 constexpr NetworkTrafficAnnotationTag DefineNetworkTrafficAnnotation(
     const char (&unique_id)[N1],
     const char (&proto)[N2]) {
   return unique_id;
 }
 
 }  // namespace net
 
 // Placeholder for unannotated usages.
 #define NO_TRAFFIC_ANNOTATION_YET \
-  net::DefineNetworkTrafficAnnotation("Undefined", "Nothing here yet.")
+  net::DefineNetworkTrafficAnnotation("undefined", "Nothing here yet.")
+
+#define MISSING_TRAFFIC_ANNOTATION     \
+  net::DefineNetworkTrafficAnnotation( \
+      "missing", "Function called without traffic annotation.")
 
 #endif  // NET_TRAFFIC_ANNOTATION_NETWORK_TRAFFIC_ANNOTATION_H_