Add UMA logging for target audio bitrate

webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc

Index: webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc
diff --git a/webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc b/webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc
index a1366a9b88557f531ecdc753558cd62b1abbaefb..b9d4cdd7d11a3786de4306ff3b91ddef05c246a3 100644
--- a/webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc
+++ b/webrtc/modules/audio_coding/main/acm2/codec_owner_unittest.cc
@@ -100,6 +100,8 @@ TEST_F(CodecOwnerTest, VerifyCngFrames) {
 
 TEST_F(CodecOwnerTest, ExternalEncoder) {
   MockAudioEncoderMutable external_encoder;
+  EXPECT_CALL(external_encoder, GetTargetBitrate())
+      .WillRepeatedly(Return(-1));  // Flag adaptive bitrate (doesn't matter).
   codec_owner_.SetEncoders(&external_encoder, -1, VADNormal, -1);
   const int kSampleRateHz = 8000;
   const int kPacketSizeSamples = kSampleRateHz / 100;