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

net/tools/quic/end_to_end_test.cc

Index: net/tools/quic/end_to_end_test.cc
diff --git a/net/tools/quic/end_to_end_test.cc b/net/tools/quic/end_to_end_test.cc
index 9c867a9d0db56962227e6b6634b2a2f8f38f4d05..3b2aa75b4089db000a031efd44081c8c5c06841b 100644
--- a/net/tools/quic/end_to_end_test.cc
+++ b/net/tools/quic/end_to_end_test.cc
@@ -73,7 +73,6 @@ using net::test::QuicSentPacketManagerPeer;
 using net::test::QuicSessionPeer;
 using net::test::QuicSpdySessionPeer;
 using net::test::ReliableQuicStreamPeer;
-using net::test::ValueRestore;
 using net::test::kClientDataStreamId1;
 using net::test::kInitialSessionFlowControlWindowForTest;
 using net::test::kInitialStreamFlowControlWindowForTest;
@@ -1343,7 +1342,7 @@ TEST_P(EndToEndTest, SetIndependentMaxIncomingDynamicStreamsLimits) {
 }
 
 TEST_P(EndToEndTest, NegotiateCongestionControl) {
-  ValueRestore<bool> old_flag(&FLAGS_quic_allow_bbr, true);
+  FLAGS_quic_allow_bbr = true;
   // Disable this flag because if connection uses multipath sent packet manager,
   // static_cast here does not work.
   FLAGS_quic_enable_multipath = false;