NetEq: Create an audio interruption metric

This CL adds a new metric to NetEq, which logs whenever a loss
concealment event has lasted longer than 150 ms (an "interruption").
The number of such events, as well as the sum length of them, is kept
in a SampleCounter, which can be queried at any time.

Any initial PLC at the beginning of a call, before the first packet is
decoded, is ignored.

Unit tests and piping to neteq_rtpplay are included.

Bug: webrtc:10549
Change-Id: I8a224a34254c47c74317617f420f6de997232d88
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/132796
Reviewed-by: Minyue Li <minyue@webrtc.org>
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27781}
diff --git a/modules/audio_coding/neteq/neteq_impl.cc b/modules/audio_coding/neteq/neteq_impl.cc
index fcb09be..ad6becc 100644
--- a/modules/audio_coding/neteq/neteq_impl.cc
+++ b/modules/audio_coding/neteq/neteq_impl.cc
@@ -822,6 +822,9 @@
   switch (operation) {
     case kNormal: {
       DoNormal(decoded_buffer_.get(), length, speech_type, play_dtmf);
+      if (length > 0) {
+        stats_->DecodedOutputPlayed();
+      }
       break;
     }
     case kMerge: {