Make latency traces more useful

test/cpp/microbenchmarks/bm_fullstack.cc

@@ -620,6 +620,7 @@ static void BM_StreamingPingPongMsgs(benchmark::State& state) {
     }
 
     while (state.KeepRunning()) {
+      GPR_TIMER_SCOPE("BenchmarkCycle", 0);
       request_rw->Write(send_request, tag(0));   // Start client send
       response_rw.Read(&recv_request, tag(1));   // Start server recv
       request_rw->Read(&recv_response, tag(2));  // Start client recv