stats: expose minPlayoutDelay as nonstandard stat

This currently only exists as a goog legacy stat and has no spec
equivalent according to
  https://docs.google.com/document/d/1z-D4SngG36WPiMuRvWeTMN7mWQXrf1XKZwVl3Nf1BIE/edit
Yet it is useful to debug issues sometimes. Exposing it as a
nonstandard stat will make it show up in chrome://webrtc-internals,
removing a need to switch to the legacy stats API there.

BUG=webrtc:14118

Change-Id: I506357ad54ff33df3ba46fb81558aa32187ac8e9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264420
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37055}
diff --git a/pc/rtc_stats_collector_unittest.cc b/pc/rtc_stats_collector_unittest.cc
index c64c523..586d07f 100644
--- a/pc/rtc_stats_collector_unittest.cc
+++ b/pc/rtc_stats_collector_unittest.cc
@@ -2156,6 +2156,7 @@
   video_media_info.receivers[0].estimated_playout_ntp_timestamp_ms =
       absl::nullopt;
   video_media_info.receivers[0].decoder_implementation_name = "";
+  video_media_info.receivers[0].min_playout_delay_ms = 50;
 
   RtpCodecParameters codec_parameters;
   codec_parameters.payload_type = 42;
@@ -2204,6 +2205,7 @@
   // `expected_video.last_packet_received_timestamp` should be undefined.
   // `expected_video.content_type` should be undefined.
   // `expected_video.decoder_implementation` should be undefined.
+  expected_video.min_playout_delay = 0.05;
 
   ASSERT_TRUE(report->Get(expected_video.id()));
   EXPECT_EQ(