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.
+// Class designed to behave like enum to be included in RTP header structs.
+struct VideoContentType {
+  // Common content types used outside of experiments.
+  static const VideoContentType UNSPECIFIED;

[sprang_webrtc, 2017/07/26 14:13:42]

Maybe declare these as constexpr instead?

[ilnik, 2017/07/26 14:49:48]

In that case, I have to initialize it right here, but the class declaration is
yet incomplete here.

+  static const VideoContentType SCREENSHARE;
+
+  operator uint8_t() const;

[sprang_webrtc, 2017/07/26 14:13:42]

Is this really needed? Would prefer to have the code access content_type (or a
getter method) directly.

[ilnik, 2017/07/26 14:49:48]

That is done, so we could replace this class with a plain enum class as it was
before, once we decide to remove all this non-standardized staff.

+
+  // No conversion constructor because otherwise this struct and many structs
+  // it's included into will be considered 'complex' and many chromium style
+  // errors will be generated.
+
+  uint8_t operator=(const uint8_t& value);
+  bool operator==(const VideoContentType& other);
+  bool operator==(const uint8_t& value);
+
+  void SetExperimentId(const uint8_t& experiment_id);
+  void SetSimulcastId(const uint8_t& simulcast_id);

[sprang_webrtc, 2017/07/26 14:13:42]

Pass uint8_t parameters by value rather than reference, here and above.

[ilnik, 2017/07/26 14:49:48]

Done.

+
+  uint8_t GetExperimentId();
+  uint8_t GetSimulcastId();
+
+  bool IsScreenshare();

[sprang_webrtc, 2017/07/26 14:13:42]

Looks like these three methods can be const?

[ilnik, 2017/07/26 14:49:48]

Done.

+
+  static bool IsValidContentType(uint8_t content_type);
+
+  uint8_t content_type;

[sprang_webrtc, 2017/07/26 14:13:42]

Make it private and have a setter method?

[ilnik, 2017/07/26 14:49:48]

For some usages it's easier to have it accessible (like getting a slicing
index). 

 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_VIDEO_VIDEO_CONTENT_TYPE_H_