Add quic_test_loopback used for tests only.

net/tools/quic/quic_server_test.cc

Index: net/tools/quic/quic_server_test.cc
diff --git a/net/tools/quic/quic_server_test.cc b/net/tools/quic/quic_server_test.cc
index 6c0037a3e85589c3be97e445e79439ae40836316..5c923d9bd44bd5a096cdf4f5928b048ba3807db8 100644
--- a/net/tools/quic/quic_server_test.cc
+++ b/net/tools/quic/quic_server_test.cc
@@ -10,6 +10,7 @@
 #include "net/quic/platform/api/quic_logging.h"
 #include "net/quic/platform/api/quic_socket_address.h"
 #include "net/quic/platform/api/quic_test.h"
+#include "net/quic/platform/api/quic_test_loopback.h"
 #include "net/quic/test_tools/crypto_test_utils.h"
 #include "net/quic/test_tools/mock_quic_dispatcher.h"
 #include "net/tools/quic/quic_epoll_alarm_factory.h"
@@ -124,7 +125,9 @@ TEST_F(QuicServerEpollInTest, ProcessBufferedCHLOsOnEpollin) {
           DoAll(testing::Assign(&more_chlos, false), testing::Return(false)));
 
   // Send a packet to trigger epoll event.
-  int fd = socket(AF_INET, SOCK_DGRAM | SOCK_NONBLOCK, IPPROTO_UDP);
+  int fd = socket(
+      AddressFamilyUnderTest() == IpAddressFamily::IP_V4 ? AF_INET : AF_INET6,
+      SOCK_DGRAM | SOCK_NONBLOCK, IPPROTO_UDP);
   ASSERT_LT(0, fd);
 
   char buf[1024];