Add an ALSA output to the motown audio server.

services/media/audio/audio_output_manager.cc

Index: services/media/audio/audio_output_manager.cc
diff --git a/services/media/audio/audio_output_manager.cc b/services/media/audio/audio_output_manager.cc
index 59e4ff38a2052c2a748e307355851b6f87412eb3..703d3e7b66ee941b28f97b31a4b9fb7f38d2fdaa 100644
--- a/services/media/audio/audio_output_manager.cc
+++ b/services/media/audio/audio_output_manager.cc
@@ -9,6 +9,9 @@
 #include "services/media/audio/audio_server_impl.h"
 #include "services/media/audio/audio_track_to_output_link.h"
 #include "services/media/audio/platform/generic/throttle_output.h"
+#if defined(OS_LINUX)
+#include "services/media/audio/platform/linux/alsa_output.h"
+#endif
 
 namespace mojo {
 namespace media {
@@ -27,6 +30,34 @@ AudioOutputManager::~AudioOutputManager() {
   DCHECK(!thread_pool_);
 }
 
+void AudioOutputManager::CreateAlsaOutputs() {
+#if defined(OS_LINUX)
+  // TODO(johngro): Do better than this.  If we really want to support
+  // Linux/ALSA as a platform, we should be creating one output for each
+  // physical output in the system, matching our configuration to the physical
+  // output's configuration, and disabling resampling at the ALSA level.
+  //
+  // If we could own the output entirely and bypass the mixer to achieve lower
+  // latency, that would be even better.
+  AudioOutputPtr audio_out(audio::AlsaOutput::New(this));
+  if (!audio_out) { return; }
+
+  AlsaOutput* alsa_out = static_cast<AlsaOutput*>(audio_out.get());
+  DCHECK(alsa_out);
+
+  LpcmMediaTypeDetailsPtr config(LpcmMediaTypeDetails::New());
+  config->frames_per_second = 48000;
+  config->samples_per_frame = 2;
+  config->sample_format = LpcmSampleFormat::SIGNED_16;
+
+  if (alsa_out->Configure(config.Pass()) != MediaResult::OK) {
+    return;
+  }
+
+  outputs_.emplace(audio_out);
+#endif
+}
+
 MediaResult AudioOutputManager::Init() {
   // Step #1: Initialize the mixing thread pool.
   //
@@ -43,6 +74,7 @@ MediaResult AudioOutputManager::Init() {
   // platform.  Right now, we just create some hardcoded default outputs and
   // leave it at that.
   outputs_.emplace(audio::ThrottleOutput::New(this));
+  CreateAlsaOutputs();
 
   // Step #3: Being monitoring for plug/unplug events for pluggable audio
   // output devices.