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

webrtc/modules/video_coding/codecs/vp8/vp8_impl.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 908 matching lines @@
         PopulateCodecSpecific(&codec_specific, tl_configs[stream_idx], *pkt,
                               stream_idx, input_image.timestamp());
         break;
       }
     }
     encoded_images_[encoder_idx]._timeStamp = input_image.timestamp();
     encoded_images_[encoder_idx].capture_time_ms_ =
         input_image.render_time_ms();
     encoded_images_[encoder_idx].rotation_ = input_image.rotation();
     encoded_images_[encoder_idx].content_type_ =
-        (codec_.mode == kScreensharing) ? VideoContentType::SCREENSHARE
-                                        : VideoContentType::UNSPECIFIED;
+        (codec_.mode == kScreensharing) ? VideoContentType::Screenshare()
+                                        : VideoContentType::Unspecified();
     encoded_images_[encoder_idx].timing_.flags = TimingFrameFlags::kInvalid;
 
     int qp = -1;
     vpx_codec_control(&encoders_[encoder_idx], VP8E_GET_LAST_QUANTIZER_64, &qp);
     temporal_layers_[stream_idx]->FrameEncoded(
         encoded_images_[encoder_idx]._length, qp);
     if (send_stream_[stream_idx]) {
       if (encoded_images_[encoder_idx]._length > 0) {
         TRACE_COUNTER_ID1("webrtc", "EncodedFrameSize", encoder_idx,
                           encoded_images_[encoder_idx]._length);
@@ skipping 309 matching lines @@
   buffer_pool_.Release();
   inited_ = false;
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
 const char* VP8DecoderImpl::ImplementationName() const {
   return "libvpx";
 }
 
 }  // namespace webrtc