Add jitterBufferTargetDelay as RTCNonStandardStatsMember to new GetStats API

Bug: webrtc:11381
Change-Id: I7df3450e50da49d178e1e3a5d9f4970672d91aac
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169120
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30758}
diff --git a/media/base/media_channel.h b/media/base/media_channel.h
index a62c618..7ca6002 100644
--- a/media/base/media_channel.h
+++ b/media/base/media_channel.h
@@ -512,6 +512,7 @@
   uint64_t concealment_events = 0;
   double jitter_buffer_delay_seconds = 0.0;
   uint64_t jitter_buffer_emitted_count = 0;
+  double jitter_buffer_target_delay_seconds = 0.0;
   uint64_t inserted_samples_for_deceleration = 0;
   uint64_t removed_samples_for_acceleration = 0;
   uint64_t fec_packets_received = 0;