Change GetServerConfig() to return const ref.

Change QuicTestClient::GetServerConfig() and SimpleQuicClient::GetServerConfig()
to return const ref instead of value in order to eliminate a copy.  This is only
used in one test file, where operator[] cannot be used any longer as it is not
constant.

Change QuicTestClient::GetServerConfig() to require that
QuicCryptoClientConfig::server_config_ to be set otherwise it crashes.  This is
safe since this method is only called by tests internally, and there are no
callers in Chrome.

Also remove unused QuicCryptoServerConfig::tag_value_map.

PiperOrigin-RevId: 378863306

quic/core/crypto/quic_crypto_server_config.h

diff --git a/quic/core/crypto/quic_crypto_server_config.h b/quic/core/crypto/quic_crypto_server_config.h
index 4f3ad08..15ce0f2 100644
--- a/quic/core/crypto/quic_crypto_server_config.h
+++ b/quic/core/crypto/quic_crypto_server_config.h
@@ -507,9 +507,6 @@
     // one-to-one, with the tags in |kexs| from the parent class.
     std::vector<std::unique_ptr<AsynchronousKeyExchange>> key_exchanges;
 
-    // tag_value_map contains the raw key/value pairs for the config.
-    QuicTagValueMap tag_value_map;
-
     // channel_id_enabled is true if the config in |serialized| specifies that
     // ChannelIDs are supported.
     bool channel_id_enabled;

quic/test_tools/quic_test_client.cc

diff --git a/quic/test_tools/quic_test_client.cc b/quic/test_tools/quic_test_client.cc
index bc1142d..598e14c 100644
--- a/quic/test_tools/quic_test_client.cc
+++ b/quic/test_tools/quic_test_client.cc
@@ -618,16 +618,12 @@
       ->cert_sct();
 }
 
-QuicTagValueMap QuicTestClient::GetServerConfig() const {
+const QuicTagValueMap& QuicTestClient::GetServerConfig() const {
   QuicCryptoClientConfig* config = client_->crypto_config();
-  QuicCryptoClientConfig::CachedState* state =
+  const QuicCryptoClientConfig::CachedState* state =
       config->LookupOrCreate(client_->server_id());
   const CryptoHandshakeMessage* handshake_msg = state->GetServerConfig();
-  if (handshake_msg != nullptr) {
-    return handshake_msg->tag_value_map();
-  } else {
-    return QuicTagValueMap();
-  }
+  return handshake_msg->tag_value_map();
 }
 
 bool QuicTestClient::connected() const {

quic/test_tools/quic_test_client.h

diff --git a/quic/test_tools/quic_test_client.h b/quic/test_tools/quic_test_client.h
index e498e8e..fd42046 100644
--- a/quic/test_tools/quic_test_client.h
+++ b/quic/test_tools/quic_test_client.h
@@ -281,8 +281,8 @@
   // or the empty std::string if no signed timestamp was presented.
   const std::string& cert_sct() const;
 
-  // Get the server config map.
-  QuicTagValueMap GetServerConfig() const;
+  // Get the server config map.  Server config must exist.
+  const QuicTagValueMap& GetServerConfig() const;
 
   void set_auto_reconnect(bool reconnect) { auto_reconnect_ = reconnect; }