Allow calling Args and ArgNames in any order.

src/benchmark_register.cc

@@ -422,7 +422,11 @@ Benchmark* Benchmark::ThreadPerCpu() {
 void Benchmark::SetName(const char* name) { name_ = name; }
 
 int Benchmark::ArgsCnt() const {
-  return args_.empty() ? -1 : static_cast<int>(args_.front().size());
+  if (args_.empty()) {
+    if (arg_names_.empty()) return -1;
+    return static_cast<int>(arg_names_.size());
+  }
+  return static_cast<int>(args_.front().size());
 }
 
 //=============================================================================//

test/reporter_output_test.cc

@@ -73,7 +73,7 @@ void BM_arg_name(benchmark::State& state) {
   while (state.KeepRunning()) {
   }
 }
-BENCHMARK(BM_arg_name)->Arg(3)->ArgName("first");
+BENCHMARK(BM_arg_name)->ArgName("first")->Arg(3);
 ADD_CASES(TC_ConsoleOut, {{"^BM_arg_name/first:3 %console_report$"}});
 ADD_CASES(TC_JSONOut, {{"\"name\": \"BM_arg_name/first:3\",$"}});
 ADD_CASES(TC_CSVOut, {{"^\"BM_arg_name/first:3\",%csv_report$"}});