Use ProcessReverseStream in VoiceEngines OutputMixer

webrtc/voice_engine/output_mixer.cc

Index: webrtc/voice_engine/output_mixer.cc
diff --git a/webrtc/voice_engine/output_mixer.cc b/webrtc/voice_engine/output_mixer.cc
index 1c9525a1ab64c0de5f57ba79677f6ee00cd4cc7f..fa4d2a4889b8b0b2b856a4e201adeb45cf7318c1 100644
--- a/webrtc/voice_engine/output_mixer.cc
+++ b/webrtc/voice_engine/output_mixer.cc
@@ -516,14 +516,7 @@ OutputMixer::DoOperationsOnCombinedSignal(bool feed_data_to_apm)
 
     // --- Far-end Voice Quality Enhancement (AudioProcessing Module)
     if (feed_data_to_apm) {
-      // Convert from mixing to AudioProcessing sample rate, similarly to how it
-      // is done on the send side. Downmix to mono.
-      AudioFrame frame;
-      frame.num_channels_ = 1;
-      frame.sample_rate_hz_ = _audioProcessingModulePtr->input_sample_rate_hz();
-      RemixAndResample(_audioFrame, &audioproc_resampler_, &frame);
-
-      if (_audioProcessingModulePtr->AnalyzeReverseStream(&frame) != 0) {
+      if (_audioProcessingModulePtr->ProcessReverseStream(&_audioFrame) != 0) {

[peah-webrtc, 2016/03/09 22:07:54]

Do we know the implications of this? This changes the APM input from being mono
to being stereo. How is this handled inside APM? Do we downmix to mono before
doing AEC, AGC and AECM processing? If not, afaics this change will actually
double the complexity for these subcomponents as the APM applies separate
instances of these for each channel. On top of that, this may trigger a bug
related to how the processing is applied on the capture channels.

Lets discuss the implications of this change.

[peah-webrtc, 2016/03/10 10:49:30]

After offline discussions: I think this change is fine as there is a
functionality in APM that also internally downmixes the signal to 1 channels. 
This changes must, however, be properly tested as the internal downmixing has
not been active (due to the code being removed in this CL) before this CL.

         WEBRTC_TRACE(kTraceWarning, kTraceVoice, VoEId(_instanceId, -1),
                      "AudioProcessingModule::AnalyzeReverseStream() => error");
         RTC_DCHECK(false);