Protect new header extension by field trial experiment to allow hardcoding it in SDP

webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc

 /*
  *  Copyright (c) 2012 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 10 matching lines @@
 #include "webrtc/base/logging.h"
 #include "webrtc/base/ptr_util.h"
 #include "webrtc/base/trace_event.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_format_video_generic.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_format_vp8.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_format_vp9.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_header_extensions.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_packet_to_send.h"
-
+#include "webrtc/system_wrappers/include/field_trial.h"
 namespace webrtc {
 
 namespace {
 constexpr size_t kRedForFecHeaderLength = 1;
 
 void BuildRedPayload(const RtpPacketToSend& media_packet,
                      RtpPacketToSend* red_packet) {
   uint8_t* red_payload = red_packet->AllocatePayload(
       kRedForFecHeaderLength + media_packet.payload_size());
   RTC_DCHECK(red_payload);
@@ skipping 279 matching lines @@
     if (video_header) {
       // Set rotation when key frame or when changed (to follow standard).
       // Or when different from 0 (to follow current receiver implementation).
       VideoRotation current_rotation = video_header->rotation;
       if (frame_type == kVideoFrameKey || current_rotation != last_rotation_ ||
           current_rotation != kVideoRotation_0)
         last_packet->SetExtension<VideoOrientation>(current_rotation);
       last_rotation_ = current_rotation;
       // Report content type only for key frames.
       if (frame_type == kVideoFrameKey &&
-          video_header->content_type != VideoContentType::UNSPECIFIED) {
+          video_header->content_type != VideoContentType::UNSPECIFIED &&
+          webrtc::field_trial::IsEnabled("WebRTC-VideoContentTypeExtension")) {
         last_packet->SetExtension<VideoContentTypeExtension>(
             video_header->content_type);
       }
     }
 
     // FEC settings.
     const FecProtectionParams& fec_params =
         frame_type == kVideoFrameKey ? key_fec_params_ : delta_fec_params_;
     if (flexfec_enabled())
       flexfec_sender_->SetFecParameters(fec_params);
@@ skipping 90 matching lines @@
   rtc::CritScope cs(&crit_);
   return retransmission_settings_;
 }
 
 void RTPSenderVideo::SetSelectiveRetransmissions(uint8_t settings) {
   rtc::CritScope cs(&crit_);
   retransmission_settings_ = settings;
 }
 
 }  // namespace webrtc