Add mojo interface for audio rendering.

content/browser/renderer_host/media/audio_output_service_impl.cc

+// Copyright 2016 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/browser/renderer_host/media/audio_output_service_impl.h"
+
+namespace content {
+
+void GetOutputControllers(
+    const RenderProcessHost::GetAudioOutputControllersCallback& callback) {
+  task_runner_->PostTask(DoGetOutputControllers, this, callback);
+}
+
+bool AudioOutputServiceImpl::HasActiveAudio() {
+  return base::AtomicRefCountIsZero(&num_playing_streams);
+}
+
+void AudioOutputServiceImpl::NotifyStreamCreated(BindingId binding) {
+  task_runner_->PostTask(Base::Bind(DoNotifyStreamCreated, this, binding));
+}
+
+void AudioOutputServiceImpl::NotifyStreamStateChanged(BindingId binding) {
+  task_runner_->PostTask(
+      Base::Bind(DoNotifyStreamStateChanged, this, binding, render_frame_id));
+}
+
+void DoGetOutputControllers(
+    const RenderProcessHost::GetAudioOutputControllersCallback& callback) {
+  RenderProcessHost::AudioOutputControllerList list;
+}
+
+void AudioOutputServiceImpl::DoNotifyStreamCreated(BindingId binding) {
+  g_audio_streams_tracker.Get().IncreaseStreamCount();
+  max_simultaneous_streams_ =
+      std::max(bindings_.size(), max_simultaneous_streams_);
+}
+
+void AudioOutputServiceImpl::RegisterStartedStream(BindingId binding);
+{
+  g_audio_streams_tracker.Get().IncreaseStreamCount();
+  if (audio_entries_.size() > max_simultaneous_streams_)
+    max_simultaneous_streams_ = audio_entries_.size();
+}
+
+}  // namespace content