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

net/quic/core/quic_connection_test.cc

Index: net/quic/core/quic_connection_test.cc
diff --git a/net/quic/core/quic_connection_test.cc b/net/quic/core/quic_connection_test.cc
index a24a222430932e8519dc4db79107d02761c04585..01156f16b12050d21fe93d05bbf93e81dff70fea 100644
--- a/net/quic/core/quic_connection_test.cc
+++ b/net/quic/core/quic_connection_test.cc
@@ -1062,6 +1062,8 @@ class QuicConnectionTest : public ::testing::TestWithParam<TestParams> {
                                    InvertPerspective(perspective));
   }
 
+  QuicFlagSaver flags_;  // Save/restore all QUIC flag values.
+
   QuicConnectionId connection_id_;
   QuicFramer framer_;
   MockEntropyCalculator entropy_calculator_;
@@ -4984,7 +4986,7 @@ TEST_P(QuicConnectionTest, SendingUnencryptedStreamDataFails) {
 TEST_P(QuicConnectionTest, EnableMultipathNegotiation) {
   // Test multipath negotiation during crypto handshake. Multipath is enabled
   // when both endpoints enable multipath.
-  ValueRestore<bool> old_flag(&FLAGS_quic_enable_multipath, true);
+  FLAGS_quic_enable_multipath = true;
   EXPECT_TRUE(connection_.connected());
   EXPECT_FALSE(QuicConnectionPeer::IsMultipathEnabled(&connection_));
   EXPECT_CALL(*send_algorithm_, SetFromConfig(_, _));