Add support for real audio output to mojo.

media/audio/audio_output_stream_sink.h

Index: media/audio/audio_output_stream_sink.h
diff --git a/media/audio/audio_output_stream_sink.h b/media/audio/audio_output_stream_sink.h
new file mode 100644
index 0000000000000000000000000000000000000000..92b55893f5a6046b9aab68060db278e40c8067aa
--- /dev/null
+++ b/media/audio/audio_output_stream_sink.h
@@ -0,0 +1,80 @@
+// Copyright 2014 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 MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_SINK_H_
+#define MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_SINK_H_
+
+#include "base/compiler_specific.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "media/audio/audio_io.h"
+#include "media/base/audio_renderer_sink.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Wrapper which exposes the browser side audio interface (AudioOutputStream) as
+// if it were a renderer side audio interface (AudioRendererSink). Note: This
+// will not work for sandboxed renderers.
+//
+// TODO(dalecurtis): Delete this class once we have a proper mojo audio service;
+// tracked by http://crbug.com/425368
+class MEDIA_EXPORT AudioOutputStreamSink
+    : NON_EXPORTED_BASE(public AudioRendererSink),
+      public AudioOutputStream::AudioSourceCallback {
+ public:
+  AudioOutputStreamSink();
+
+  // AudioRendererSink implementation.
+  virtual void Initialize(const AudioParameters& params,
+                          RenderCallback* callback) override;
+  virtual void Start() override;
+  virtual void Stop() override;
+  virtual void Pause() override;
+  virtual void Play() override;
+  virtual bool SetVolume(double volume) override;

[xhwang, 2014/10/22 16:31:53]

s/virtual//

Basically only use one of {virtual, override, final}:

https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/VTNZzizN0zo

[DaleCurtis, 2014/10/22 21:33:44]

Done.

+
+  // AudioSourceCallback implementation.
+  virtual int OnMoreData(AudioBus* dest, uint32 total_bytes_delay) override;
+  virtual void OnError(AudioOutputStream* stream) override;

[xhwang, 2014/10/22 16:31:53]

ditto

[DaleCurtis, 2014/10/22 21:33:44]

Done.

+
+ private:
+  virtual ~AudioOutputStreamSink();
+
+  // Helper methods for running AudioManager methods on the audio thread.
+  void DoStart();
+  void DoStop();
+  void DoPause();
+  void DoPlay();
+  void DoSetVolume(double volume);
+
+  // Clears |active_render_callback_| under lock, synchronously stopping render
+  // callbacks from any thread.  Must be called before Pause() and Stop()
+  // trampoline to their helper methods on the audio thread.
+  void ClearCallback();
+
+  // Parameters provided by Initialize(), cached for use on other threads.

[xhwang, 2014/10/22 16:31:53]

Can you explain the threading model of this class? We have an audio thread and a
lock, but it's not clear how this these work together.

[DaleCurtis, 2014/10/22 21:33:44]

The threading model is explained here:
https://code.google.com/p/chromium/codesearch#chromium/src/media/audio/audio_...

I can elaborate some more here if you like, but we haven't typically added such
comments to the implementors of that interface.

[xhwang, 2014/10/22 21:37:31]

I didn't know that. Thanks! Agreed that we don't need to duplicate the docs
here.

+  AudioParameters params_;
+
+  // Since Initialize() is only called once for AudioRenderSinks, save the
+  // callback both here and under |active_render_callback_| which will be
+  // cleared during Pause() and Stop() to achieve "synchronous" stoppage.
+  RenderCallback* render_callback_;
+
+  // The task runner for the audio thread.
+  const scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner_;
+
+  // The actual AudioOutputStream, must only be accessed on the audio thread.
+  AudioOutputStream* stream_;
+
+  // Lock and callback for forwarding OnMoreData() calls into Render() calls.
+  base::Lock callback_lock_;
+  RenderCallback* active_render_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputStreamSink);
+};
+
+}  // namepace media
+
+#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_SINK_H_