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/include/audio_coding_module_typedefs.h

@@ -119,6 +119,8 @@ struct NetworkStatistics {
   size_t addedSamples;
   // count of the number of buffer flushes
   uint64_t packetBufferFlushes;
+  // number of samples expanded due to delayed packets
+  uint64_t delayedPacketOutageSamples;
 };
 
 }  // namespace webrtc