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

net/quic/core/quic_packet_generator_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_generator.h"
 
 #include <cstdint>
 #include <memory>
 #include <string>
 
@@ skipping 189 matching lines @@
     memset(data_array_.get(), '?', len);
     iov_.iov_base = data_array_.get();
     iov_.iov_len = len;
     return QuicIOVector(&iov_, 1, len);
   }
 
   QuicIOVector MakeIOVector(StringPiece s) {
     return ::net::MakeIOVector(s, &iov_);
   }
 
+  QuicFlagSaver flags_;  // Save/restore all QUIC flag values.
   QuicFramer framer_;
   MockRandom random_;
   SimpleBufferAllocator buffer_allocator_;
   StrictMock<MockDelegate> delegate_;
   QuicPacketGenerator generator_;
   QuicPacketCreator* creator_;
   SimpleQuicFramer simple_framer_;
   vector<SerializedPacket> packets_;
   QuicAckFrame ack_frame_;
 
@@ skipping 651 matching lines @@
   EXPECT_CALL(delegate_, OnSerializedPacket(_))
       .WillOnce(Invoke(this, &QuicPacketGeneratorTest::SavePacket));
   generator_.FlushAllQueuedFrames();
   EXPECT_FALSE(generator_.HasQueuedFrames());
   generator_.SetCurrentPath(kTestPathId1, 1, 0);
   EXPECT_EQ(kTestPathId1, QuicPacketCreatorPeer::GetCurrentPath(creator_));
 }
 
 }  // namespace test
 }  // namespace net