Add operator<<(ostream, AlternativeService) for test output formatting.

net/http/http_server_properties.h

Index: net/http/http_server_properties.h
diff --git a/net/http/http_server_properties.h b/net/http/http_server_properties.h
index eef795beb32844e132722675f068e6cd93ec256d..7efbf1ab5369500c835dd651d0c3781995ae3a14 100644
--- a/net/http/http_server_properties.h
+++ b/net/http/http_server_properties.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include <map>
+#include <ostream>
 #include <string>
 #include <tuple>
 #include <vector>
@@ -109,6 +110,10 @@ struct NET_EXPORT AlternativeService {
   uint16_t port;
 };
 
+NET_EXPORT_PRIVATE std::ostream& operator<<(
+    std::ostream& os,
+    const AlternativeService& alternative_service);
+
 struct NET_EXPORT AlternativeServiceInfo {
   AlternativeServiceInfo() : alternative_service() {}