Add a mojo implementation of AudioOutputIPC.

content/public/common/content_features.cc

Index: content/public/common/content_features.cc
diff --git a/content/public/common/content_features.cc b/content/public/common/content_features.cc
index 1436426c834edee4716410d64a9562265bcf5ca5..64e61c89cb3cce5e9d79452022710d04d68dccd7 100644
--- a/content/public/common/content_features.cc
+++ b/content/public/common/content_features.cc
@@ -226,6 +226,11 @@ const base::Feature kTokenBinding{"token-binding",
 const base::Feature kTouchpadAndWheelScrollLatching{
     "TouchpadAndWheelScrollLatching", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Use MojoAudioOutputIPC and RenderFrameAudioOutputStreamFactory rather than
+// AudioMessageFilter and AudioRendererHost.
+const base::Feature kUseMojoAudioOutputStreamFactory{
+    "UseMojoAudioOutputStreamFactory", base::FEATURE_DISABLED_BY_DEFAULT};

[o1ka, 2017/04/20 10:35:59]

This is "enabling a feature behind a flag", so it needs to be mentioned in the
CL description.

I would do it in a separate CL though (see
https://codereview.chromium.org/2108673004 as an example of switching to a
feature later): it would be cheaper to revert. 

Do we want to have separate experiments for input and output? Since mirroring
connects outputs with inputs they are not totally independent. We'll end up with
4 experimental subsets instead of 2.

[Max Morin, 2017/05/05 13:10:58]

I removed the feature.
The hope is that this will be done before input. :)

+
 // Enables VR UI.
 const base::Feature kVrShell{"VrShell", base::FEATURE_DISABLED_BY_DEFAULT};