Add mojo interface+impl for audio stream control.

media/mojo/services/mojo_audio_output_provider.cc

+// 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.
+
+#include "media/mojo/services/mojo_audio_output_provider.h"
+
+#include <utility>
+
+namespace media {
+
+MojoAudioOutputProvider::MojoAudioOutputProvider(
+    AudioOutputProviderRequest request,
+    CreateDelegateCallback create_delegate_callback,
+    DeleterCallback deleter_callback)
+    : binding_(this, request),
+      create_delegate_callback_(std::move(create_delegate_callback)),
+      deleter_callback_(std::move(deleter_callback)) {
+  DCHECK(create_delegate_callback_);
+  DCHECK(deleter_callback_);
+}
+
+MojoAudioOutputProvider::~MojoAudioOutputProvider() {}
+
+void MojoAudioOutputProvider::Acquire(AudioOutputRequest request,

[DaleCurtis, 2017/03/06 17:56:12]

Is it possible to setup the provider object to repeatedly vend instances? Or are
they 1-shot always?

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

I don't think we want to skip the authorization check. I also don't think we'd
make the renderer-side use a provider multiple times. I'll CC guido for
implications the spec has on this.

+                                      const AudioParameters& params,
+                                      AcquireCallback acquire_callback) {
+  if (audio_output_) {
+    LOG(ERROR) << "Output acquired twice.";

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

Shouldn't |acquire_callback| run here? Or an error should be signaled. Otherwise
a client does not get any reply.

How common is the pattern like this with a factory interface which cannot be
reused?

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

Right, I changed this to unbinding the binder and calling the deleter.
Not common I think?

[o1ka, 2017/03/07 23:31:06]

I mean - have you seen examples in mojo services implementation? It looks kind
of odd and I do not really like it when shooting in the foot is so easy. But
with your last change it will crush quickly and it's simple - that's good.

[Max Morin, 2017/03/08 07:38:29]

From what I gather from the spec (though I am no expert), I don't think it ever
makes sense to reuse a permissions check. Because of this, I don't want to allow
it. I agree it's ugly though.

+    return;
+  }
+  audio_output_.emplace(std::move(request),
+                        base::Bind(create_delegate_callback, params),
+                        std::move(acquire_callback),
+                        base::Bind(deleter_callback, base::Unretained(this)));

[DaleCurtis, 2017/03/06 17:56:12]

hmm, is Unretained necessary here? You're binding arguments here.

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

It's actually not. I removed it.

+}
+
+}  // namespace media