Adding a test utility to print QuicTagValueMaps.

net/quic/core/quic_utils.h

Index: net/quic/core/quic_utils.h
diff --git a/net/quic/core/quic_utils.h b/net/quic/core/quic_utils.h
index 8fe06d127209671b69b6fa31ac333830a1f41dbb..b80e845b895678a976803c00a77f015cc89dd664 100644
--- a/net/quic/core/quic_utils.h
+++ b/net/quic/core/quic_utils.h
@@ -94,6 +94,9 @@ class NET_EXPORT_PRIVATE QuicUtils {
   static QuicTagVector ParseQuicConnectionOptions(
       const std::string& connection_options);
 
+  // ListTags prints all of the tags in |tag_map| using TagToString.
+  static std::string ListTags(QuicTagValueMap tag_map);
+
   // Returns PeerAddressChangeType as a std::string.
   static std::string PeerAddressChangeTypeToString(PeerAddressChangeType type);