Pass camera facing info to audio client

content/browser/renderer_host/media/media_stream_manager.h

Index: content/browser/renderer_host/media/media_stream_manager.h
diff --git a/content/browser/renderer_host/media/media_stream_manager.h b/content/browser/renderer_host/media/media_stream_manager.h
index 8747539857459c586e05796386bea7f8223dc1c1..07344373e99f622950700d7513d3b76f8d28e3f6 100644
--- a/content/browser/renderer_host/media/media_stream_manager.h
+++ b/content/browser/renderer_host/media/media_stream_manager.h
@@ -45,6 +45,7 @@
 #include "content/common/media/media_devices.h"
 #include "content/common/media/media_stream_options.h"
 #include "content/public/browser/media_request_state.h"
+#include "media/base/video_facing.h"
 
 namespace media {
 class AudioManager;
@@ -97,6 +98,8 @@ class CONTENT_EXPORT MediaStreamManager
   // Used to access MediaDevicesManager.
   MediaDevicesManager* media_devices_manager();
 
+  void SetVideoCaptureObserver(media::VideoCaptureObserver* capture_observer);

[chfremer1, 2017/01/25 18:13:44]

I recommend that we indicate to the reader that this method is part of the
construction+configuration interface of MediaStreamManager, as opposed to the
interface intended for "usage by its regular clients". 

In my opinion, the cleanest way to express this in C++ would be to explicitly
define and expose an interface containing only the methods that are intended for
"usage by regular clients", and SetVideoCaptureObserver() would probably not be
a part of that. This approach has the extra advantage of allowing us to easily
mock out MediaStreamManager when testing its clients.

If that is too much work, the "cheap" way would be to express this information
in a comment.

Either way, we should express the following information to the reader:
* At what time of the lifecycle of MediaStreamManager is it legal to call this
method.
* On what thread would it need to be called (probably the same as the
constructor?)
* Is it legal to call it more than once? Potentially setting |capture_observer|
back to nullptr? (This would be useful for clients who cannot guarantee that
|capture_observer| outlives the MediaStreamManager instance.)
* Is it legal to not call it at all?
* On what thread will the callbacks to |capture_observer| arrive?

[shenghao, 2017/01/29 10:21:01]

Done.

+
   // Creates a new media access request which is identified by a unique string
   // that's returned to the caller. This will trigger the infobar and ask users
   // for access to the device. |render_process_id| and |render_frame_id| are