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

net/quic/chromium/quic_network_transaction_unittest.cc

Index: net/quic/chromium/quic_network_transaction_unittest.cc
diff --git a/net/quic/chromium/quic_network_transaction_unittest.cc b/net/quic/chromium/quic_network_transaction_unittest.cc
index 006f78513926cfa5241c41e6381895c77bef2cb2..aabcf52ea7dc18e1e333ec179e4f8abbe6a9d89d 100644
--- a/net/quic/chromium/quic_network_transaction_unittest.cc
+++ b/net/quic/chromium/quic_network_transaction_unittest.cc
@@ -665,6 +665,7 @@ class QuicNetworkTransactionTest
     SendRequestAndExpectHttpResponseFromProxy("hello from http", true, 443);
   }
 
+  QuicFlagSaver flags_;  // Save/restore all QUIC flag values.
   MockClock* clock_;  // Owned by QuicStreamFactory after CreateSession.
   QuicTestPacketMaker client_maker_;
   QuicTestPacketMaker server_maker_;
@@ -2559,10 +2560,6 @@ TEST_P(QuicNetworkTransactionTest, QuicServerPush) {
 }
 
 TEST_P(QuicNetworkTransactionTest, QuicForceHolBlocking) {
-  ValueRestore<bool> old_v35_flag(&FLAGS_quic_enable_version_35,
-                                  FLAGS_quic_enable_version_35);
-  ValueRestore<bool> old_v36_flag(&FLAGS_quic_enable_version_36,
-                                  FLAGS_quic_enable_version_36);
   FLAGS_quic_enable_version_35 = true;
   FLAGS_quic_enable_version_36 = true;
   params_.quic_force_hol_blocking = true;