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

webrtc/video/end_to_end_tests.cc

 /*
  *  Copyright (c) 2013 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.
  */
 #include <algorithm>
@@ skipping 2773 matching lines @@
       {
         rtc::CritScope lock(&crit_);
         num_frames_received_ = 0;
       }
     }
 
     rtc::CriticalSection crit_;
     int num_frames_received_ GUARDED_BY(&crit_);
   } test;
 
+  test::ScopedFieldTrials override_field_trials(
+      "WebRTC-VideoContentTypeExtension/Enabled/");
   metrics::Reset();
 
   Call::Config send_config(test.GetSenderCallConfig());
   CreateSenderCall(send_config);
   Call::Config recv_config(test.GetReceiverCallConfig());
   CreateReceiverCall(recv_config);
   receive_transport_.reset(test.CreateReceiveTransport());
   send_transport_.reset(test.CreateSendTransport(sender_call_.get()));
   send_transport_->SetReceiver(receiver_call_->Receiver());
   receive_transport_->SetReceiver(sender_call_->Receiver());
@@ skipping 64 matching lines @@
   const bool kEnabledRtx = false;
   const bool kEnabledRed = true;
   const bool kScreenshare = false;
   VerifyHistogramStats(kEnabledRtx, kEnabledRed, kScreenshare);
 }
 
 TEST_F(EndToEndTest, VerifyHistogramStatsWithScreenshare) {
   const bool kEnabledRtx = false;
   const bool kEnabledRed = false;
   const bool kScreenshare = true;
+  test::ScopedFieldTrials override_field_trials(
+      "WebRTC-VideoContentTypeExtension/Enabled/");
   VerifyHistogramStats(kEnabledRtx, kEnabledRed, kScreenshare);
 }
 
 void EndToEndTest::TestSendsSetSsrcs(size_t num_ssrcs,
                                      bool send_single_ssrc_first) {
   class SendsSetSsrcs : public test::EndToEndTest {
    public:
     SendsSetSsrcs(const uint32_t* ssrcs,
                   size_t num_ssrcs,
                   bool send_single_ssrc_first)
@@ skipping 2025 matching lines @@
     std::unique_ptr<VideoEncoder> encoder_;
     std::unique_ptr<VideoDecoder> decoder_;
     rtc::CriticalSection crit_;
     int recorded_frames_ GUARDED_BY(crit_);
   } test(this);
 
   RunBaseTest(&test);
 }
 
 }  // namespace webrtc