Add POLQA to low bandwidth audio test

webrtc/audio/test/low_bandwidth_audio_test.cc

Index: webrtc/audio/test/low_bandwidth_audio_test.cc
diff --git a/webrtc/audio/test/low_bandwidth_audio_test.cc b/webrtc/audio/test/low_bandwidth_audio_test.cc
index de955f75e19c936b98e61692f832d62254d8ffcc..bd2dc384ddd39a7f53813a1cbd18b85bad337f75 100644
--- a/webrtc/audio/test/low_bandwidth_audio_test.cc
+++ b/webrtc/audio/test/low_bandwidth_audio_test.cc
@@ -10,6 +10,7 @@
 
 #include <algorithm>
 
+#include "gflags/gflags.h"
 #include "webrtc/audio/test/low_bandwidth_audio_test.h"
 #include "webrtc/common_audio/wav_file.h"
 #include "webrtc/test/gtest.h"
@@ -23,8 +24,8 @@ constexpr int kExtraRecordTimeMs = 500;
 // Large bitrate by default.
 const webrtc::CodecInst kDefaultCodec{120, "OPUS", 48000, 960, 2, 64000};
 
-// The best that can be done with PESQ.
-constexpr int kAudioFileBitRate = 16000;
+DEFINE_int32(sampling_frequency, 16000,
+             "Sampling frequency (Hz) of the produced audio files.");
 }
 
 namespace webrtc {
@@ -44,14 +45,16 @@ size_t AudioQualityTest::GetNumFlexfecStreams() const {
 }
 
 std::string AudioQualityTest::AudioInputFile() {
-  return test::ResourcePath("voice_engine/audio_tiny16", "wav");
+  return test::ResourcePath("voice_engine/audio_tiny" +
+                            std::to_string(FLAGS_sampling_frequency / 1000),
+                            "wav");
 }
 
 std::string AudioQualityTest::AudioOutputFile() {
   const ::testing::TestInfo* const test_info =
       ::testing::UnitTest::GetInstance()->current_test_info();
-  return webrtc::test::OutputPath() +
-      "LowBandwidth_" + test_info->name() + ".wav";
+  return webrtc::test::OutputPath() + "LowBandwidth_" + test_info->name() +
+      "_" + std::to_string(FLAGS_sampling_frequency / 1000) + ".wav";
 }
 
 std::unique_ptr<test::FakeAudioDevice::Capturer>
@@ -62,7 +65,7 @@ std::unique_ptr<test::FakeAudioDevice::Capturer>
 std::unique_ptr<test::FakeAudioDevice::Renderer>
     AudioQualityTest::CreateRenderer() {
   return test::FakeAudioDevice::CreateBoundedWavFileWriter(
-      AudioOutputFile(), kAudioFileBitRate);
+      AudioOutputFile(), FLAGS_sampling_frequency);
 }
 
 void AudioQualityTest::OnFakeAudioDevicesCreated(