Expose jitter buffer flushes metric in new getStats api.

Origin trial experiment proposal (new statistic part):
https://docs.google.com/document/d/1stYIZhEmDZ7NJF9gjjsM66eLFJUdc-14a3QutrFbIwI/edit?ts=5bf5535c#

Bug: chromium:907113
Change-Id: I1d005291f9b47665f70c26148dbdcbb55564bef8
Reviewed-on: https://webrtc-review.googlesource.com/c/111505
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Ruslan Burakov <kuddai@google.com>
Cr-Commit-Position: refs/heads/master@{#25768}
diff --git a/api/stats/rtcstats.h b/api/stats/rtcstats.h
index f65df28..7fd0d84 100644
--- a/api/stats/rtcstats.h
+++ b/api/stats/rtcstats.h
@@ -295,15 +295,6 @@
     is_defined_ = true;
     return value_;
   }
-  T& operator=(const RTCStatsMember<T>& other) {
-    RTC_DCHECK(other.is_defined_);
-    // Shouldn't be attempting to assign an RTCNonStandardStatsMember to an
-    // RTCStatsMember or vice versa.
-    RTC_DCHECK(is_standardized() == other.is_standardized());
-    value_ = other.value_;
-    is_defined_ = true;
-    return value_;
-  }
 
   // Value getters.
   T& operator*() {
@@ -348,6 +339,11 @@
       : RTCStatsMember<T>(std::move(other)) {}
 
   bool is_standardized() const override { return false; }
+
+  T& operator=(const T& value) { return RTCStatsMember<T>::operator=(value); }
+  T& operator=(const T&& value) {
+    return RTCStatsMember<T>::operator=(std::move(value));
+  }
 };
 }  // namespace webrtc
 
diff --git a/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index dc9da72..8496f8c 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -308,6 +308,9 @@
   RTCStatsMember<double> total_samples_duration;
   RTCStatsMember<uint64_t> concealed_samples;
   RTCStatsMember<uint64_t> concealment_events;
+  // Non-standard audio-only member
+  // TODO(kuddai): Add descriptoin to standard. crbug.com/webrtc/10042
+  RTCNonStandardStatsMember<uint64_t> jitter_buffer_flushes;
 };
 
 // https://w3c.github.io/webrtc-stats/#pcstats-dict*