Add an ALSA output to the motown audio server.

services/media/audio/platform/linux/alsa_output.h

Index: services/media/audio/platform/linux/alsa_output.h
diff --git a/services/media/audio/platform/linux/alsa_output.h b/services/media/audio/platform/linux/alsa_output.h
new file mode 100644
index 0000000000000000000000000000000000000000..1da2ca27de2c16d856ec3a1ea4fc94183e524462
--- /dev/null
+++ b/services/media/audio/platform/linux/alsa_output.h
@@ -0,0 +1,65 @@
+// Copyright 2015 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.
+
+#ifndef SERVICES_MEDIA_AUDIO_PLATFORM_LINUX_ALSA_OUTPUT_H_
+#define SERVICES_MEDIA_AUDIO_PLATFORM_LINUX_ALSA_OUTPUT_H_
+
+#include <alsa/asoundlib.h>
+#include <memory>
+
+#include "mojo/services/media/common/cpp/linear_transform.h"
+#include "mojo/services/media/common/interfaces/media_types.mojom.h"
+#include "services/media/audio/audio_output.h"
+#include "services/media/audio/platform/generic/standard_output_base.h"
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+class AlsaOutput : public StandardOutputBase {
+ public:
+  static AudioOutputPtr New(AudioOutputManager* manager);
+  ~AlsaOutput() override;
+
+  MediaResult Configure(LpcmMediaTypeDetailsPtr config);
+
+ protected:
+  explicit AlsaOutput(AudioOutputManager* manager);
+
+  // AudioOutput implementation
+  MediaResult Init() override;
+  void Cleanup() override;
+
+  // StandardOutputBase implementation
+  bool StartMixJob(MixJob* job, const LocalTime& process_start) override;
+  bool FinishMixJob(const MixJob& job) override;
+
+ private:
+  void FillMixBufWithSilence(uint32_t frames);
+  void HandleAlsaError(snd_pcm_sframes_t code);
+  void HandleAsError(snd_pcm_sframes_t code);
+  void HandleAsUnderflow();
+
+  snd_pcm_t* alsa_device_ = nullptr;
+  snd_pcm_format_t alsa_format_;
+
+  LinearTransform::Ratio frames_per_tick_;
+  uint8_t silence_byte_;
+
+  std::unique_ptr<uint8_t> mix_buf_;
+  uint32_t mix_buf_frames_;
+
+  bool primed_ = false;
+  bool local_to_output_known_ = false;
+  LinearTransform local_to_output_;
+  uint32_t local_to_output_gen_ = MixJob::INVALID_GENERATION + 1;
+  int64_t frames_sent_;
+};
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo
+
+#endif  // SERVICES_MEDIA_AUDIO_PLATFORM_LINUX_ALSA_OUTPUT_H_
+