Add a new QuicFlagSaver class for saving/restoring the values of QUIC flags in tests.

net/quic/core/quic_crypto_client_stream_test.cc

 // Copyright (c) 2012 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.
 
 #include "net/quic/core/quic_crypto_client_stream.h"
 
 #include <memory>
 
 #include "net/quic/core/crypto/aes_128_gcm_12_encrypter.h"
 #include "net/quic/core/crypto/quic_decrypter.h"
@@ skipping 291 matching lines @@
                                &server_connection_, &server_session);
     CHECK(server_session);
     server_session_.reset(server_session);
     CryptoTestUtils::FakeServerOptions options;
     CryptoTestUtils::SetupCryptoServerConfigForTest(
         server_connection_->clock(), server_connection_->random_generator(),
         server_session_->config(), &server_crypto_config_, options);
     FLAGS_enable_quic_stateless_reject_support = true;
   }
 
+  QuicFlagSaver flags_;  // Save/restore all QUIC flag values.
+
   MockQuicConnectionHelper helper_;
   MockAlarmFactory alarm_factory_;
 
   // Client crypto stream state
   PacketSavingConnection* client_connection_;
   std::unique_ptr<TestQuicSpdyClientSession> client_session_;
   QuicCryptoClientConfig client_crypto_config_;
 
   // Server crypto stream state
   PacketSavingConnection* server_connection_;
   std::unique_ptr<TestQuicSpdyServerSession> server_session_;
   QuicCryptoServerConfig server_crypto_config_;
   QuicCompressedCertsCache server_compressed_certs_cache_;
   QuicServerId server_id_;
 };
 
 TEST_F(QuicCryptoClientStreamStatelessTest, StatelessReject) {
-  ValueRestore<bool> old_flag(&FLAGS_enable_quic_stateless_reject_support,
-                              true);
+  FLAGS_enable_quic_stateless_reject_support = true;
 
   QuicCryptoClientConfig::CachedState* client_state =
       client_crypto_config_.LookupOrCreate(server_id_);
 
   EXPECT_FALSE(client_state->has_server_designated_connection_id());
   EXPECT_CALL(*client_session_, OnProofValid(testing::_));
 
   InitializeFakeStatelessRejectServer();
   AdvanceHandshakeWithFakeServer();
 
@@ skipping 13 matching lines @@
       client_state->GetNextServerDesignatedConnectionId();
   QuicConnectionId expected_id =
       server_session_->connection()->random_generator()->RandUint64();
   EXPECT_EQ(expected_id, server_designated_id);
   EXPECT_FALSE(client_state->has_server_designated_connection_id());
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net