Revert of Remove the last piece of deprecated synchronous IO code.

media/audio/mac/audio_manager_mac.cc

 // Copyright (c) 2012 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 "media/audio/mac/audio_manager_mac.h"
 
 #include <CoreAudio/AudioHardware.h>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 656 matching lines @@
   // work correctly.
   int output_channels = input_params.channels();
   ChannelLayout channel_layout = input_params.channel_layout();
   if (!has_valid_input_params || output_channels > hardware_channels) {
     output_channels = hardware_channels;
     channel_layout = GuessChannelLayout(output_channels);
     if (channel_layout == CHANNEL_LAYOUT_UNSUPPORTED)
       channel_layout = CHANNEL_LAYOUT_DISCRETE;
   }
 
+  const int input_channels =
+      has_valid_input_params ? input_params.input_channels() : 0;
+  if (input_channels > 0) {
+    // TODO(xians): given the limitations of the AudioOutputStream
+    // back-ends used with synchronized I/O, we hard-code to stereo.
+    // Specifically, this is a limitation of AudioSynchronizedStream which
+    // can be removed as part of the work to consolidate these back-ends.
+    channel_layout = CHANNEL_LAYOUT_STEREO;
+  }
+
   return AudioParameters(
       AudioParameters::AUDIO_PCM_LOW_LATENCY, channel_layout, output_channels,
-      hardware_sample_rate, 16, buffer_size, AudioParameters::NO_EFFECTS);
+      input_channels, hardware_sample_rate, 16, buffer_size,
+      AudioParameters::NO_EFFECTS);
 }
 
 void AudioManagerMac::InitializeOnAudioThread() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   power_observer_.reset(new AudioPowerObserver());
 }
 
 void AudioManagerMac::ShutdownOnAudioThread() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   output_device_listener_.reset();
@@ skipping 57 matching lines @@
 void AudioManagerMac::ReleaseInputStream(AudioInputStream* stream) {
   input_streams_.remove(stream);
   AudioManagerBase::ReleaseInputStream(stream);
 }
 
 AudioManager* CreateAudioManager(AudioLogFactory* audio_log_factory) {
   return new AudioManagerMac(audio_log_factory);
 }
 
 }  // namespace media