trivial change to remove the hard coding to mono as the output channel layout in MSAP.

content/renderer/media/media_stream_audio_processor.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/media_stream_audio_processor.h"
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/metrics/field_trial.h"
 #include "content/public/common/content_switches.h"
@@ skipping 358 matching lines @@
   DCHECK(source_params.IsValid());
 
   // Create and initialize audio converter for the source data.
   // When the webrtc AudioProcessing is enabled, the sink format of the
   // converter will be the same as the post-processed data format, which is
   // 32k mono for desktops and 16k mono for Android. When the AudioProcessing
   // is disabled, the sink format will be the same as the source format.
   const int sink_sample_rate = audio_processing_ ?
       kAudioProcessingSampleRate : source_params.sample_rate();
   const media::ChannelLayout sink_channel_layout = audio_processing_ ?
-      media::CHANNEL_LAYOUT_MONO : source_params.channel_layout();
+      media::GuessChannelLayout(kAudioProcessingNumberOfChannel) :
+      source_params.channel_layout();
 
   // WebRtc AudioProcessing requires 10ms as its packet size. We use this
   // native size when processing is enabled. While processing is disabled, and
   // the source is running with a buffer size smaller than 10ms buffer, we use
   // same buffer size as the incoming format to avoid extra FIFO for WebAudio.
   int sink_buffer_size =  sink_sample_rate / 100;
   if (!audio_processing_ &&
       source_params.frames_per_buffer() < sink_buffer_size) {
     sink_buffer_size = source_params.frames_per_buffer();
   }
@@ skipping 98 matching lines @@
 }
 
 bool MediaStreamAudioProcessor::IsAudioTrackProcessingEnabled() const {
   const std::string group_name =
       base::FieldTrialList::FindFullName("MediaStreamAudioTrackProcessing");
   return group_name == "Enabled" || CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableAudioTrackProcessing);
 }
 
 }  // namespace content