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

webrtc/video/video_send_stream_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>  // max
@@ skipping 314 matching lines @@
           RtpExtension(RtpExtension::kVideoContentTypeUri,
                        test::kVideoContentTypeExtensionId));
       encoder_config->content_type = VideoEncoderConfig::ContentType::kScreen;
     }
 
     void PerformTest() override {
       EXPECT_TRUE(Wait()) << "Timed out while waiting for single RTP packet.";
     }
   } test;
 
-  test::ScopedFieldTrials override_field_trials(
-      "WebRTC-VideoContentTypeExtension/Enabled/");
   RunBaseTest(&test);
 }
 
 class FakeReceiveStatistics : public NullReceiveStatistics {
  public:
   FakeReceiveStatistics(uint32_t send_ssrc,
                         uint32_t last_sequence_number,
                         uint32_t cumulative_lost,
                         uint8_t fraction_lost)
       : lossy_stats_(new LossyStatistician(last_sequence_number,
@@ skipping 2992 matching lines @@
     rtc::CriticalSection crit_;
     uint32_t max_bitrate_bps_ GUARDED_BY(&crit_);
     bool first_packet_sent_ GUARDED_BY(&crit_);
     rtc::Event bitrate_changed_event_;
   } test;
 
   RunBaseTest(&test);
 }
 
 }  // namespace webrtc