Add qualityLimitationResolutionChanges stat

Implements the stat qualityLimitationResolutionChanges [1].

[1] https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-qualitylimitationresolutionchanges

Bug: webrtc:10935
Change-Id: I391f2be5958a96b442e32c40ab7043752f3f71dd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150882
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@google.com>
Cr-Commit-Position: refs/heads/master@{#29113}
diff --git a/media/base/media_channel.h b/media/base/media_channel.h
index 0f502d3..9cc7876 100644
--- a/media/base/media_channel.h
+++ b/media/base/media_channel.h
@@ -562,6 +562,8 @@
   // https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-qualitylimitationdurations
   std::map<webrtc::QualityLimitationReason, int64_t>
       quality_limitation_durations_ms;
+  // https://w3c.github.io/webrtc-stats/#dom-rtcoutboundrtpstreamstats-qualitylimitationresolutionchanges
+  uint32_t quality_limitation_resolution_changes = 0;
   int avg_encode_ms = 0;
   int encode_usage_percent = 0;
   uint32_t frames_encoded = 0;