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

net/tools/quic/quic_simple_client_bin.cc

Index: net/tools/quic/quic_simple_client_bin.cc
diff --git a/net/tools/quic/quic_simple_client_bin.cc b/net/tools/quic/quic_simple_client_bin.cc
index 742f0f6626c812df8480f8607d7c01295695ced8..6599c8699553293494d64a86c8a15b93089b3d9a 100644
--- a/net/tools/quic/quic_simple_client_bin.cc
+++ b/net/tools/quic/quic_simple_client_bin.cc
@@ -127,6 +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"