Add UMA logging for target audio bitrate

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

Index: webrtc/modules/audio_coding/main/acm2/codec_manager.cc
diff --git a/webrtc/modules/audio_coding/main/acm2/codec_manager.cc b/webrtc/modules/audio_coding/main/acm2/codec_manager.cc
index cad6ee908939b9c1523924f5b2d1b372b7077f1d..d28dcc6ff5e6d63a2fbba52a7873c4869fce93cf 100644
--- a/webrtc/modules/audio_coding/main/acm2/codec_manager.cc
+++ b/webrtc/modules/audio_coding/main/acm2/codec_manager.cc
@@ -13,6 +13,8 @@
 #include "webrtc/base/checks.h"
 #include "webrtc/engine_configurations.h"
 #include "webrtc/modules/audio_coding/main/acm2/acm_codec_database.h"
+#include "webrtc/modules/audio_coding/main/acm2/acm_common_defs.h"
+#include "webrtc/system_wrappers/interface/metrics.h"
 #include "webrtc/system_wrappers/interface/trace.h"
 
 namespace webrtc {
@@ -312,6 +314,9 @@ int CodecManager::RegisterEncoder(const CodecInst& send_codec) {
   // Check if a change in Rate is required.
   if (send_codec.rate != send_codec_inst_.rate) {
     codec_owner_.SpeechEncoder()->SetTargetBitrate(send_codec.rate);
+    RTC_HISTOGRAM_COUNTS_100(
+        HISTOGRAM_NAME_AUDIO_TARGET_BITRATE_IN_KBPS,
+        codec_owner_.SpeechEncoder()->GetTargetBitrate() / 1000);
     send_codec_inst_.rate = send_codec.rate;
   }