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

net/quic/test_tools/quic_test_utils.cc

Index: net/quic/test_tools/quic_test_utils.cc
diff --git a/net/quic/test_tools/quic_test_utils.cc b/net/quic/test_tools/quic_test_utils.cc
index 6069fa3fc6c6001e7e248abcae6c8cd567d0e4b0..1514f2d28df230b3172c9e548d0ac19b704b78d8 100644
--- a/net/quic/test_tools/quic_test_utils.cc
+++ b/net/quic/test_tools/quic_test_utils.cc
@@ -97,6 +97,18 @@ QuicPacket* BuildUnsizedDataPacket(QuicFramer* framer,
                         header.public_header.packet_number_length);
 }
 
+QuicFlagSaver::QuicFlagSaver() {
+#define QUIC_FLAG(type, flag, value) CHECK_EQ(value, flag);
+#include "net/quic/core/quic_flags_list.h"
+#undef QUIC_FLAG
+}
+
+QuicFlagSaver::~QuicFlagSaver() {
+#define QUIC_FLAG(type, flag, value) flag = value;
+#include "net/quic/core/quic_flags_list.h"
+#undef QUIC_FLAG
+}
+
 uint64_t SimpleRandom::RandUint64() {
   unsigned char hash[base::kSHA1Length];
   base::SHA1HashBytes(reinterpret_cast<unsigned char*>(&seed_), sizeof(seed_),