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

webrtc/api/video/video_content_type.h

Index: webrtc/api/video/video_content_type.h
diff --git a/webrtc/api/video/video_content_type.h b/webrtc/api/video/video_content_type.h
index 5c468c079d35ea2d20c115234cf38d7e7fcd42bd..45e3cac21b100c39e8a71389c5650d6c55c7ed34 100644
--- a/webrtc/api/video/video_content_type.h
+++ b/webrtc/api/video/video_content_type.h
@@ -15,10 +15,33 @@
 
 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;
+  static const VideoContentType SCREENSHARE;
+
+  operator uint8_t() const;
+
+  // 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=(uint8_t value);
+  bool operator==(const VideoContentType& other);
+  bool operator==(uint8_t value);
+
+  void SetExperimentId(uint8_t experiment_id);
+  void SetSimulcastId(uint8_t simulcast_id);
+
+  uint8_t GetExperimentId() const;
+  uint8_t GetSimulcastId() const;
+
+  bool IsScreenshare() const;
+
+  static bool IsValidContentType(uint8_t content_type);
+
+  uint8_t content_type;

[sprang_webrtc, 2017/08/24 09:13:16]

Should we add a SetScreenshare(bool) as well and make |content_type| private?

[ilnik, 2017/08/25 12:35:07]

Can't do. It will make this class to be considered complex by chromium style
analyzer, which makes it and everything it's included in (e.g. RTPVideoHeader
and bunch others) to require a out-of-line constructors.

This will require a broad refactoring of core rtp related code. I would rather
not do that for such a simple reason.

SetScreenshare is not needed, as this struct is treated as an enum in encoders:
it's simply initialized to UNSPECIFIED or SCREENSHARE.

 };
 
 }  // namespace webrtc