Domain Reliability: Measure backoff/retry time to collectors.

components/domain_reliability/context.cc

Index: components/domain_reliability/context.cc
diff --git a/components/domain_reliability/context.cc b/components/domain_reliability/context.cc
index ad63776574ce075d2724654c9bebe8174d292da9..e33d056ec9cdf25f783e10738f39e630a4121e20 100644
--- a/components/domain_reliability/context.cc
+++ b/components/domain_reliability/context.cc
@@ -260,6 +260,8 @@ void DomainReliabilityContext::OnUploadComplete(
   DCHECK(!upload_time_.is_null());
   UMA_HISTOGRAM_MEDIUM_TIMES("DomainReliability.UploadDuration",
                              now - upload_time_);
+  UMA_HISTOGRAM_LONG_TIMES("DomainReliability.UploadCollectorRetryDelay",
+                           scheduler_.last_collector_retry_delay());
   last_upload_time_ = upload_time_;
   upload_time_ = base::TimeTicks();
 }