Move declaration of --export_perf_results_new_api.

By declaring and defining the flag in a separate and reusable library
it can be used by other main() implementations as well.

Bug: b/237982523
Change-Id: Ia5445ee6e85bc1d536bee2ddd842439f8832116b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/285480
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Auto-Submit: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#38765}

test/test_flags.cc

@@ -43,3 +43,8 @@ ABSL_FLAG(std::string,
           "Path where the test perf metrics should be stored using "
           "api/test/metrics/metric.proto proto format. File will contain "
           "MetricsSet as a root proto");
+
+ABSL_FLAG(bool,
+          export_perf_results_new_api,
+          false,
+          "Tells to initialize new API for exporting performance metrics");

test/test_flags.h

@@ -19,5 +19,6 @@ ABSL_DECLARE_FLAG(std::string, force_fieldtrials);
 ABSL_DECLARE_FLAG(std::vector<std::string>, plot);
 ABSL_DECLARE_FLAG(std::string, isolated_script_test_perf_output);
 ABSL_DECLARE_FLAG(std::string, webrtc_test_metrics_output_path);
+ABSL_DECLARE_FLAG(bool, export_perf_results_new_api);
 
 #endif  // TEST_TEST_FLAGS_H_

test/test_main_lib.cc

@@ -86,11 +86,6 @@ ABSL_FLAG(std::string,
           "",
           "Path to output an empty JSON file which Chromium infra requires.");
 
-ABSL_FLAG(bool,
-          export_perf_results_new_api,
-          false,
-          "Tells to initialize new API for exporting performance metrics");
-
 ABSL_FLAG(bool, logs, true, "print logs to stderr");
 ABSL_FLAG(bool, verbose, false, "verbose logs to stderr");