[Adaptation] Disable inital frame drop for simuclast/svc

Bug: chromium:1080789
Change-Id: I72bbee4ac21302d15b6c54abea48d665e8ef6922
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174808
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31212}

video/video_stream_encoder.cc

@@ -1652,7 +1652,12 @@ void VideoStreamEncoder::OnBitrateUpdated(DataRate target_bitrate,
 }
 
 bool VideoStreamEncoder::DropDueToSize(uint32_t pixel_count) const {
-  if (!stream_resource_manager_.DropInitialFrames() ||
+  bool simulcast_or_svc =
+      (send_codec_.codecType == VideoCodecType::kVideoCodecVP9 &&
+       send_codec_.VP9().numberOfSpatialLayers > 1) ||
+      send_codec_.numberOfSimulcastStreams > 1;
+
+  if (simulcast_or_svc || !stream_resource_manager_.DropInitialFrames() ||
       !encoder_target_bitrate_bps_.has_value()) {
     return false;
   }