Teach `benchmark.mojo` to save the collected trace file to disk.

apps/benchmark/run_args.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef APPS_BENCHMARK_RUN_ARGS_H_
 #define APPS_BENCHMARK_RUN_ARGS_H_
 
 #include <string>
 #include <vector>
 
 #include "apps/benchmark/measurements.h"
+#include "base/files/file_path.h"
 #include "base/time/time.h"
 
 namespace benchmark {
 
 // Represents arguments for a run of the benchmark app.
 struct RunArgs {
   std::string app;
   base::TimeDelta duration;
   std::vector<Measurement> measurements;
+  bool write_output_file;
+  base::FilePath output_file_path;
 
   RunArgs();
   ~RunArgs();
 };
 
 // Parses the arguments representation from the format provided by
 // ApplicationImpl::args(). Returns true iff the arguments were correctly parsed
 // and stored in |result|.
 bool GetRunArgs(const std::vector<std::string>& input_args, RunArgs* result);
 
 }  // namespace benchmark
 
 #endif  // APPS_BENCHMARK_RUN_ARGS_H_