Add a mojo implementation of AudioOutputIPC.

content/renderer/media/audio_ipc_factory.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 CONTENT_RENDERER_MEDIA_AUDIO_IPC_FACTORY_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_IPC_FACTORY_H_
+
+#include <memory>
+
+#include "base/containers/flat_map.h"
+#include "base/memory/ref_counted.h"
+#include "content/common/media/renderer_audio_output_stream_factory.mojom.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace media {
+class AudioOutputIPC;
+}
+
+namespace content {
+
+class AudioIPCFactory {

[o1ka, 2017/04/20 10:35:59]

RendererAudioIPCFactory?

[Max Morin, 2017/05/05 13:10:58]

Most stuff in renderer/ is not prefixed renderer. It seems redundant to me.

+ public:
+  AudioIPCFactory(
+      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner);
+  ~AudioIPCFactory();
+
+  // The following functions may be called on any thread:
+
+  static AudioIPCFactory* get() {

[o1ka, 2017/04/20 10:35:59]

Get(), and move implementation to .cc?

[Max Morin, 2017/05/05 13:10:58]

I couldn't find the rule against this in the style guide, checking
https://google.github.io/styleguide/cppguide.html#Inline_Functions and
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md....
https://www.chromium.org/developers/coding-style/cpp-dos-and-donts mentions
simple accessors. This is as simple as a function could be, and also an
accessor, so it should be fine.

[o1ka, 2017/05/15 13:27:08]

it has DCHECK, so technically it's not a "simple accessor" => should be named
Get()

[Max Morin, 2017/05/16 15:51:35]

It doesn't have the DCHECK in later patch sets (since it's null in some tests
involving render frames) :).

+    DCHECK(instance_);
+    return instance_;
+  }
+
+  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner() const {
+    return io_task_runner_;
+  }
+
+  // Enables |this| to create AudioOutputIPCs for the specified frame. It is

[o1ka, 2017/04/20 10:35:59]

Looking at CreateAudioOutputIPC() it's not clear how it enables it?

[Max Morin, 2017/05/05 13:10:58]

Does it matter?

+  // automatically deregistered on frame destruction.

[o1ka, 2017/04/20 10:35:59]

What does "automatically" mean here? Doesn't frame call
DeregisterRemoteFactory() on destruction?

[Max Morin, 2017/05/05 13:10:58]

Right, I had to change this and didn't update the comment :).

+  void RegisterRemoteFactory(

[o1ka, 2017/04/20 10:35:59]

"RemoteFactory" sounds confusing, it's hard to associate it with any concept by
this name. "FrameStreamFactory" maybe? Also, do you plan to overload it for
input?

[Max Morin, 2017/05/05 13:10:58]

A remote factory is a factory that is remote, in the sense of being in another
process. "FrameStreamFactory" can be associated with frames and streams, but the
most important thing about the factory is that it's the one in the browser
process. "IPCStreamFactory" would make sense, but it's almost the same as the
name for this class. WDYT of MojoStreamFactory?
I wouldn't overload it, I suppose it's open if input should go into this class
or in a separate one. If it goes into this class, I will put "Input" or "Output"
in all the names to clarify.

+      int frame_id,
+      mojom::RendererAudioOutputStreamFactoryPtr factory_ptr);
+
+  void DeregisterRemoteFactory(int frame_id);
+
+  // The following functions shall only be called on the IO thread:
+
+  std::unique_ptr<media::AudioOutputIPC> CreateAudioOutputIPC(
+      int frame_id) const;
+
+  mojom::RendererAudioOutputStreamFactory* GetRemoteFactory(int frame_id);

[o1ka, 2017/04/20 10:35:59]

It's used by MojoAudioOutputIPC only, right?
WDYT of passing it as a callback instead of exposing it as public?

[Max Morin, 2017/05/05 13:10:58]

Done.

+
+ private:
+  using StreamFactoryMap =
+      base::flat_map<int, mojom::RendererAudioOutputStreamFactoryPtr>;
+
+  void RegisterRemoteFactoryOnIOThread(
+      int frame_id,
+      mojom::RendererAudioOutputStreamFactoryPtrInfo factory_ptr_info);
+
+  void DeregisterRemoteFactoryOnIOThread(int frame_id);
+
+  // Maps frame id to the corresponding factory.
+  StreamFactoryMap factory_ptrs_;
+
+  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
+
+  // Global instance, set in constructor and unset in destructor.
+  static AudioIPCFactory* instance_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_IPC_FACTORY_H_