Add a mojo implementation of AudioOutputIPC.

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index 46e27ce6204e9f36b676151b74e71ec688cdb022..1a61ad41e092e6c46fb6d892409c92c90206d8f4 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -8,9 +8,11 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <map>
 #include <memory>
 #include <set>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "base/cancelable_callback.h"
@@ -21,6 +23,7 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/observer_list.h"
+#include "base/optional.h"
 #include "base/strings/string16.h"
 #include "base/threading/thread_checker.h"
 #include "base/timer/timer.h"
@@ -40,6 +43,7 @@
 #include "content/public/renderer/render_thread.h"
 #include "content/renderer/gpu/compositor_dependencies.h"
 #include "content/renderer/layout_test_dependencies.h"
+#include "content/renderer/media/audio_ipc_factory.h"
 #include "gpu/ipc/client/gpu_channel_host.h"
 #include "media/media_features.h"
 #include "mojo/public/cpp/bindings/associated_binding.h"
@@ -314,10 +318,6 @@ class CONTENT_EXPORT RenderThreadImpl
     return audio_input_message_filter_.get();
   }
 
-  AudioMessageFilter* audio_message_filter() {
-    return audio_message_filter_.get();
-  }
-
   MidiMessageFilter* midi_message_filter() {
     return midi_message_filter_.get();
   }
@@ -635,6 +635,10 @@ class CONTENT_EXPORT RenderThreadImpl
   scoped_refptr<AecDumpMessageFilter> aec_dump_message_filter_;
 #endif
 
+  // Provides AudioOutputIPC objects for audio output devices. It either uses
+  // |audio_message_filter_| for this or provides MojoAudioOutputIPC objects.
+  base::Optional<AudioIPCFactory> audio_ipc_factory_;

[o1ka, 2017/05/11 10:58:41]

Would unique_ptr<> be enough for that?
And under which conditions it's uninitialized?

[Max Morin, 2017/05/11 15:31:18]

There's no need for unique_ptr, since Optional is enough :). unique_ptr is an
extra allocation, so I default to using Optional, and use unique_ptr if needed.
Added a comment about initialization.

+
   // Used on the render thread.
   std::unique_ptr<VideoCaptureImplManager> vc_manager_;