Pass camera facing info to audio client

media/base/video_facing.h

 // Copyright 2017 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.
 
 #ifndef MEDIA_BASE_VIDEO_FACING_H_
 #define MEDIA_BASE_VIDEO_FACING_H_
 
 namespace media {
 
 // Facing mode for video capture.
 enum VideoFacingMode {
   MEDIA_VIDEO_FACING_NONE = 0,
   MEDIA_VIDEO_FACING_USER,
   MEDIA_VIDEO_FACING_ENVIRONMENT,
 
-  NUM_MEDIA_VIDEO_FACING_MODE
+  NUM_MEDIA_VIDEO_FACING_MODES
+};
+
+// Clients interested in video capture events can implement this interface
+// and register the observers to MediaStreamManager or VideoCaptureManager.
+class VideoCaptureObserver {
+ public:
+  virtual ~VideoCaptureObserver() {}
+  virtual void OnVideoCaptureStarted(VideoFacingMode facing) = 0;
+  virtual void OnVideoCaptureStopped(VideoFacingMode facing) = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_FACING_H_