Add mojo interface+impl for audio stream control.

media/mojo/services/mojo_audio_output_provider.h

+// Copyright 2017 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_MOJO_SERVICES_MOJO_AUDIO_OUTPUT_PROVIDER_H_
+#define MEDIA_MOJO_SERVICES_MOJO_AUDIO_OUTPUT_PROVIDER_H_
+
+#include <memory>
+#include <string>
+
+// Provides a single AudioOutput, given the audio parameters to use.
+
+#include "base/threading/thread_checker.h"
+#include "media/audio/audio_output_delegate.h"
+#include "media/mojo/interfaces/audio_output.mojom.h"
+#include "media/mojo/services/media_mojo_export.h"
+#include "media/mojo/services/mojo_audio_output.h"
+#include "mojo/public/cpp/bindings/binding.h"
+
+namespace media {
+
+class MEDIA_MOJO_EXPORT MojoAudioOutputProvider
+    : public mojom::AudioOutputProvider {
+ public:
+  using CreateDelegateCallback =
+      base::OnceCallback<std::unique_ptr<AudioOutputDelegate>(
+          const AudioParameters& params,
+          AudioOutputDelegate::EventHandler*)>;
+  using DeleterCallback = base::OnceCallback<void(mojom::AudioOutputProvider*)>;
+
+  // |create_delegate_callback| is used to obtain an AudioOutputDelegate for the
+  // AudioOutput when it's initialized and |deleter_callback| is called when
+  // this class should be removed (stream ended/error). |deleter_callback| is
+  // required to destroy |this| synchronously.
+  MojoAudioOutputProvider(AudioOutputProviderRequest request,
+                          CreateDelegateCallback create_delegate_callback,
+                          DeleterCallback deleter_callback);
+
+  ~MojoAudioOutputProvider() override;
+
+ private:
+  // mojom::AudioOutput implementation.
+  void Acquire(AudioParameters params,
+               AcquireCallback acquire_callback) override;
+
+  // The callback for the Acquire() must be stored until the response is ready.
+  AcquireCallback acquire_callback_;
+
+  base::Optional<AudioOutput> audio_output_;
+  mojo::Binding<AudioOutputProvider*> binding_;

[o1ka, 2017/03/07 00:49:24]

How will delete AudioOutputProvider if a connection is closed before Acquire()
is called? 

[Max Morin, 2017/03/07 11:23:17]

I fixed this (added connection error handler to binding).

+  DeleterCallback deleter_callback_;
+  base::ThreadChecker thread_checker_;

[o1ka, 2017/03/07 00:49:24]

Not used?

[Max Morin, 2017/03/07 11:23:16]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(MojoAudioOutputProvider);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_MOJO_SERVICES_MOJO_AUDIO_OUTPUT_PROVIDER_H_