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

webrtc/modules/rtp_rtcp/source/rtp_utility.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_utility.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_utility.cc b/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
index 4b5ecfa6983d61cba3ebaf9adc74496858c7f4bf..ab963d369c97fe37e290a8972f96a4848277bd9c 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
@@ -244,7 +244,7 @@ bool RtpHeaderParser::Parse(RTPHeader* header,
 
   // May not be present in packet.
   header->extension.hasVideoContentType = false;
-  header->extension.videoContentType = VideoContentType::UNSPECIFIED;
+  header->extension.videoContentType = VideoContentType::Unspecified();
 
   header->extension.has_video_timing = false;
   header->extension.video_timing = {0u, 0u, 0u, 0u, 0u, 0u, false};
@@ -452,11 +452,9 @@ void RtpHeaderParser::ParseOneByteExtensionHeader(
           //   |  ID   | len=0 | Content type  |
           //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
-          if (ptr[0] <
-              static_cast<uint8_t>(VideoContentType::TOTAL_CONTENT_TYPES)) {
+          if (VideoContentType::IsValidContentType(ptr[0])) {
             header->extension.hasVideoContentType = true;
-            header->extension.videoContentType =
-                static_cast<VideoContentType>(ptr[0]);
+            header->extension.videoContentType = ptr[0];
           }
           break;
         }