Add a mojo implementation of AudioOutputIPC.

content/renderer/media/audio_ipc_factory.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 "content/renderer/media/audio_ipc_factory.h"
+
+#include <utility>
+
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "content/renderer/media/audio_message_filter.h"
+#include "content/renderer/media/mojo_audio_output_ipc.h"
+#include "services/service_manager/public/cpp/interface_provider.h"
+
+namespace content {
+
+AudioIPCFactory* AudioIPCFactory::instance_ = nullptr;
+
+AudioIPCFactory::AudioIPCFactory(
+    const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,
+    AudioMessageFilter* audio_message_filter)
+    : audio_message_filter_(audio_message_filter),
+      io_task_runner_(io_task_runner) {
+  // TODO(maxmorin): In the future, set |audio_message_filter_| to nullptr based
+  // on a feature.
+  DCHECK(!instance_);
+  instance_ = this;
+}
+
+AudioIPCFactory::~AudioIPCFactory() {
+  DCHECK_EQ(instance_, this);
+  instance_ = nullptr;
+}
+
+bool AudioIPCFactory::UsingMojoFactories() const {
+  return audio_message_filter_ == nullptr;
+}
+
+std::unique_ptr<media::AudioOutputIPC> AudioIPCFactory::CreateAudioOutputIPC(
+    int frame_id) const {
+  if (UsingMojoFactories())
+    return base::MakeUnique<MojoAudioOutputIPC>(base::Bind(
+        &AudioIPCFactory::GetRemoteFactory, base::Unretained(this), frame_id));
+  return audio_message_filter_->CreateAudioOutputIPC(frame_id);
+}
+
+void AudioIPCFactory::RegisterRemoteFactory(
+    int frame_id,
+    mojom::RendererAudioOutputStreamFactoryPtr factory) {
+  DCHECK(UsingMojoFactories());
+  // PassInterface unbinds the message pipe from the current thread. This
+  // allows us to bind it to the IO thread.
+  // Unretained is safe because |this| is owned by the RenderThreadImpl which is

[o1ka, 2017/05/11 10:58:40]

If "not being destroyed ever" is a requirement for the class to work correctly -
add a comment into the header and DCHECK that destructor is never called? And
rephrase these comments?

[Max Morin, 2017/05/11 15:31:17]

Added header comment and updated these comments. Destructing may still make
sense in tests though. Added a comment for that.

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

It still a bit confusing, since the comment says 
|this| is leaked, but it's not leaked in test according to the destructor
comment.

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

Ok, I expanded the header comment to include the case of unit tests.

+  // leaked.
+  io_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&AudioIPCFactory::RegisterRemoteFactoryOnIOThread,
+                            base::Unretained(this), frame_id,
+                            base::Passed(factory.PassInterface())));
+}
+
+void AudioIPCFactory::MaybeDeregisterRemoteFactory(int frame_id) {
+  if (!UsingMojoFactories())
+    return;
+  if (!io_task_runner_->BelongsToCurrentThread()) {
+    // Unretained is safe because |this| is owned by the RenderThreadImpl which
+    // is leaked.
+    io_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&AudioIPCFactory::MaybeDeregisterRemoteFactory,
+                              base::Unretained(this), frame_id));
+    return;
+  }
+  factory_ptrs_.erase(frame_id);
+}
+
+mojom::RendererAudioOutputStreamFactory* AudioIPCFactory::GetRemoteFactory(
+    int frame_id) const {
+  DCHECK(io_task_runner_->BelongsToCurrentThread());
+  DCHECK(UsingMojoFactories());
+  auto it = factory_ptrs_.find(frame_id);
+  return it == factory_ptrs_.end() ? nullptr : it->second.get();
+}
+
+void AudioIPCFactory::RegisterRemoteFactoryOnIOThread(
+    int frame_id,
+    mojom::RendererAudioOutputStreamFactoryPtrInfo factory_ptr_info) {
+  DCHECK(io_task_runner_->BelongsToCurrentThread());
+  DCHECK(UsingMojoFactories());
+  std::pair<StreamFactoryMap::iterator, bool> emplace_result =
+      factory_ptrs_.emplace(frame_id,
+                            mojo::MakeProxy(std::move(factory_ptr_info)));
+
+  DCHECK(emplace_result.second) << "Attempt to register a factory for a "
+                                   "frame which already has a factory "
+                                   "registered.";
+
+  auto& emplaced_factory = emplace_result.first->second;
+  DCHECK(emplaced_factory.is_bound())
+      << "Factory is not bound to a remote implementation.";
+
+  // Unretained is safe because |this| owns the binding, so a connection error
+  // cannot trigger after destruction.
+  emplaced_factory.set_connection_error_handler(
+      base::Bind(&AudioIPCFactory::MaybeDeregisterRemoteFactory,
+                 base::Unretained(this), frame_id));
+}
+
+}  // namespace content