Turn on the trailers support flag in the toy QUIC client.

net/tools/quic/quic_client_bin.cc

Index: net/tools/quic/quic_client_bin.cc
diff --git a/net/tools/quic/quic_client_bin.cc b/net/tools/quic/quic_client_bin.cc
index 84ec757ee6467acbbdca24cb8e8a7f1fe1d0f1e1..e23bb590e1a0da598cb764c7cae5bc801fd24613 100644
--- a/net/tools/quic/quic_client_bin.cc
+++ b/net/tools/quic/quic_client_bin.cc
@@ -55,6 +55,7 @@
 #include "net/http/transport_security_state.h"
 #include "net/log/net_log.h"
 #include "net/quic/crypto/proof_verifier_chromium.h"
+#include "net/quic/quic_flags.h"
 #include "net/quic/quic_protocol.h"
 #include "net/quic/quic_server_id.h"
 #include "net/quic/quic_utils.h"
@@ -126,6 +127,8 @@ int main(int argc, char *argv[]) {
   settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
   CHECK(logging::InitLogging(settings));
 
+  FLAGS_quic_supports_trailers = true;
+
   if (line->HasSwitch("h") || line->HasSwitch("help") || urls.empty()) {
     const char* help_str =
         "Usage: quic_client [options] <url>\n"