Add a mojo implementation of AudioOutputIPC.

content/renderer/BUILD.gn

Index: content/renderer/BUILD.gn
diff --git a/content/renderer/BUILD.gn b/content/renderer/BUILD.gn
index 20c365dd9b5de84e30458e03415279290be1535b..503f317c607fcda7ee214bcc67e52dcc0a04f623 100644
--- a/content/renderer/BUILD.gn
+++ b/content/renderer/BUILD.gn
@@ -220,6 +220,8 @@ target(link_target_type, "renderer") {
     "media/audio_device_factory.h",
     "media/audio_input_message_filter.cc",
     "media/audio_input_message_filter.h",
+    "media/audio_ipc_factory.cc",
+    "media/audio_ipc_factory.h",
     "media/audio_message_filter.cc",
     "media/audio_message_filter.h",
     "media/audio_renderer_mixer_manager.cc",
@@ -238,6 +240,8 @@ target(link_target_type, "renderer") {
     "media/media_permission_dispatcher.h",
     "media/midi_message_filter.cc",
     "media/midi_message_filter.h",
+    "media/mojo_audio_output_ipc.cc",
+    "media/mojo_audio_output_ipc.h",
     "media/render_media_client.cc",
     "media/render_media_client.h",
     "media/render_media_log.cc",