Add UMA logging for target audio bitrate

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

Index: webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
diff --git a/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc b/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
index b659649096e8c583400698e16a5b1723d3b4c4dc..d914a8e19ca309ae81976c53b3226e34812cef52 100644
--- a/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
+++ b/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
@@ -23,6 +23,7 @@
 #include "webrtc/modules/audio_coding/main/acm2/call_statistics.h"
 #include "webrtc/system_wrappers/interface/critical_section_wrapper.h"
 #include "webrtc/system_wrappers/interface/logging.h"
+#include "webrtc/system_wrappers/interface/metrics.h"
 #include "webrtc/system_wrappers/interface/rw_lock_wrapper.h"
 #include "webrtc/system_wrappers/interface/trace.h"
 #include "webrtc/typedefs.h"
@@ -288,7 +289,8 @@ int AudioCodingModuleImpl::SendBitrate() const {
 
 void AudioCodingModuleImpl::SetBitRate(int bitrate_bps) {
   CriticalSectionScoped lock(acm_crit_sect_);
-
+  RTC_HISTOGRAM_COUNTS_100("WebRTC.Audio.TargetBitrateInKbps",

[kwiberg-webrtc, 2015/06/11 10:03:13]

Define a constant for this string? You use it in 3 places, and am I correct in
assuming that a misspelling wouldn't trigger a compile-time error?

[hlundin-webrtc, 2015/06/11 10:11:48]

Yes, that might be a good idea. Any suggestion on where to store it?

[kwiberg-webrtc, 2015/06/11 11:01:25]

I think my preferred solution would be for all of WebRTC to define all of these
constants in a central place---metrics.h, say. But something like
acm_common_defs.h might also work.

+                           bitrate_bps / 1000);
   if (codec_manager_.CurrentEncoder()) {
     codec_manager_.CurrentEncoder()->SetTargetBitrate(bitrate_bps);

[kwiberg-webrtc, 2015/06/11 10:03:13]

If this method would just return the bitrate the encoder actually decided to
use, we could log that too. Would that be useful?

[hlundin-webrtc, 2015/06/11 10:11:48]

That could be useful. But it would mean that it must be implemented by all
codecs, not only by those who support changing rates.

[kwiberg-webrtc, 2015/06/11 11:01:25]

Yes---but the implementation would be trivial, so it could be worth it.

But we also set the bitrate when constructing encoders (see the codec_owner.cc
diff in this CL), so maybe a dedicated method just for inquiring about the
target bitrate would be better.

   }