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}

modules/audio_coding/neteq/include/neteq.h

@@ -72,6 +72,7 @@ struct NetEqLifetimeStatistics {
   uint64_t jitter_buffer_delay_ms = 0;
   // Below stat is not part of the spec.
   uint64_t voice_concealed_samples = 0;
+  uint64_t delayed_packet_outage_samples = 0;
 };
 
 // Metrics that describe the operations performed in NetEq, and the internal