Expose delayed packet outage as a cumulative metric of samples in the new getStats API.

The stat will be exposed through origin trial described in:
https://docs.google.com/document/d/1stYIZhEmDZ7NJF9gjjsM66eLFJUdc-14a3QutrFbIwI

Change-Id: Ib191a11c6bd9e617abbe9dd82239b0c5b4e6b4e0
Bug: webrtc:10043
Reviewed-on: https://webrtc-review.googlesource.com/c/111922
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Minyue Li <minyue@webrtc.org>
Commit-Queue: Jakob Ivarsson‎ <jakobi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25802}
diff --git a/media/base/mediachannel.h b/media/base/mediachannel.h
index 04e70c5..fca6ee4 100644
--- a/media/base/mediachannel.h
+++ b/media/base/mediachannel.h
@@ -478,6 +478,8 @@
   int64_t capture_start_ntp_time_ms = -1;
   // Count of the number of buffer flushes.
   uint64_t jitter_buffer_flushes = 0;
+  // Number of samples expanded due to delayed packets.
+  uint64_t delayed_packet_outage_samples = 0;
 };
 
 struct VideoSenderInfo : public MediaSenderInfo {