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

net/quic/core/quic_packet_creator_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_packet_creator.h"
 
 #include <cstdint>
 #include <memory>
 #include <string>
 
@@ skipping 205 matching lines @@
       EncryptionLevel encryption_level,
       QuicPacketNumberLength packet_number_length) {
     return PendingRetransmission(1u, 1u, NOT_RETRANSMISSION,
                                  retransmittable_frames, has_crypto_handshake,
                                  num_padding_bytes, encryption_level,
                                  packet_number_length);
   }
 
   static const QuicStreamOffset kOffset = 1u;
 
+  QuicFlagSaver flags_;  // Save/restore all QUIC flag values.
   char buffer_[kMaxPacketSize];
   QuicFrames frames_;
   QuicFramer server_framer_;
   QuicFramer client_framer_;
   StrictMock<MockFramerVisitor> framer_visitor_;
   StrictMock<MockDelegate> delegate_;
   QuicConnectionId connection_id_;
   string data_;
   struct iovec iov_;
   MockRandom mock_random_;
@@ skipping 1090 matching lines @@
   EXPECT_CALL(delegate_,
               OnUnrecoverableError(QUIC_CRYPTO_CHLO_TOO_LARGE, _, _));
   EXPECT_QUIC_BUG(
       creator_.ConsumeData(1u, data_iovec, 0u, 0u, false, false, &frame),
       "Client hello won't fit in a single packet.");
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net