Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/api/video/video_content_type.h

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_API_VIDEO_VIDEO_CONTENT_TYPE_H_
 #define WEBRTC_API_VIDEO_VIDEO_CONTENT_TYPE_H_
 
 #include <stdint.h>
 
 namespace webrtc {
 
 enum class VideoContentType : uint8_t {
   UNSPECIFIED = 0,
   SCREENSHARE = 1,
-  TOTAL_CONTENT_TYPES  // Must be the last value in the enum.
 };
 
+namespace VideoContentTypeHelpers {

[kwiberg-webrtc, 2017/08/29 20:58:53]

"Namespace names are all lower-case." See
https://google.github.io/styleguide/cppguide.html#Namespace_Names

However, it may make more sense to make a struct with static methods instead of
a namespace; you can't open it up later and add more stuff, and there are fewer
dangerous name lookup rules.

[ilnik, 2017/08/30 07:36:06]

Great idea. Done.

+bool SetExperimentId(VideoContentType* content_type, uint8_t experiment_id);
+bool SetSimulcastId(VideoContentType* content_type, uint8_t simulcast_id);
+
+uint8_t GetExperimentId(const VideoContentType& content_type);
+uint8_t GetSimulcastId(const VideoContentType& content_type);
+
+bool IsScreenshare(const VideoContentType& content_type);
+
+bool IsValidContentType(uint8_t value);
+}  // namespace VideoContentTypeHelpers
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_VIDEO_VIDEO_CONTENT_TYPE_H_