Add optional output audio file to NetEq simulation API

Bug: webrtc:10337
Change-Id: I2e9071d4d2bd4b181d198031cf459965c9682775
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171518
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30873}

api/BUILD.gn

@@ -688,6 +688,7 @@ if (rtc_include_tests) {
         "//third_party/abseil-cpp/absl/flags:flag",
         "//third_party/abseil-cpp/absl/flags:parse",
         "//third_party/abseil-cpp/absl/strings",
+        "//third_party/abseil-cpp/absl/types:optional",
       ]
     }
   }

api/test/neteq_simulator_factory.cc

@@ -37,6 +37,7 @@ std::unique_ptr<NetEqSimulator> NetEqSimulatorFactory::CreateSimulatorFromFile(
   config.initial_dummy_packets = simulation_config.initial_dummy_packets;
   config.skip_get_audio_events = simulation_config.skip_get_audio_events;
   config.field_trial_string = simulation_config.field_trial_string;
+  config.output_audio_filename = simulation_config.output_audio_filename;
   return factory_->InitializeTestFromFile(
       std::string(event_log_filename), simulation_config.neteq_factory, config);
 }

api/test/neteq_simulator_factory.h

@@ -15,6 +15,7 @@
 #include <string>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/optional.h"
 #include "api/neteq/neteq_factory.h"
 #include "api/test/neteq_simulator.h"
 
@@ -41,6 +42,8 @@ class NetEqSimulatorFactory {
     int skip_get_audio_events = 0;
     // A WebRTC field trial string to be used during the simulation.
     std::string field_trial_string;
+    // A filename for the generated output audio file.
+    absl::optional<std::string> output_audio_filename;
     // A custom NetEqFactory can be used.
     NetEqFactory* neteq_factory = nullptr;
   };