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

webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc

 /*
  *  Copyright (c) 2016 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.
  */
 
@@ skipping 214 matching lines @@
 //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 //   |  ID   | len=0 | Content type  |
 //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 constexpr RTPExtensionType VideoContentTypeExtension::kId;
 constexpr uint8_t VideoContentTypeExtension::kValueSizeBytes;
 constexpr const char VideoContentTypeExtension::kUri[];
 
 bool VideoContentTypeExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                       VideoContentType* content_type) {
   if (data.size() == 1 &&
-      data[0] < static_cast<uint8_t>(VideoContentType::TOTAL_CONTENT_TYPES)) {
+      videocontenttypehelpers::IsValidContentType(data[0])) {
     *content_type = static_cast<VideoContentType>(data[0]);
     return true;
   }
   return false;
 }
 
 bool VideoContentTypeExtension::Write(uint8_t* data,
                                       VideoContentType content_type) {
   data[0] = static_cast<uint8_t>(content_type);
   return true;
@@ skipping 128 matching lines @@
 constexpr RTPExtensionType RtpStreamId::kId;
 constexpr const char RtpStreamId::kUri[];
 
 constexpr RTPExtensionType RepairedRtpStreamId::kId;
 constexpr const char RepairedRtpStreamId::kUri[];
 
 constexpr RTPExtensionType RtpMid::kId;
 constexpr const char RtpMid::kUri[];
 
 }  // namespace webrtc