Domain Reliability: Measure backoff/retry time to collectors.

components/domain_reliability/scheduler.h

Index: components/domain_reliability/scheduler.h
diff --git a/components/domain_reliability/scheduler.h b/components/domain_reliability/scheduler.h
index aac257ed6e8d7466b0d22269767828fc93e0dd33..22a7fd86c8e17f533a524ed8cefc825a1ab813a7 100644
--- a/components/domain_reliability/scheduler.h
+++ b/components/domain_reliability/scheduler.h
@@ -78,6 +78,13 @@ class DOMAIN_RELIABILITY_EXPORT DomainReliabilityScheduler {
   // unit tests.
   void MakeDeterministicForTesting();
 
+  // Gets the time until the next upload attempt on the last collector used.
+  // This will be 0 if the upload was a success; it does not take into account
+  // minimum_upload_delay and maximum_upload_delay.
+  base::TimeDelta last_collector_retry_delay() const {
+    return last_collector_retry_delay_;
+  }
+
  private:
   void MaybeScheduleUpload();
 
@@ -115,6 +122,10 @@ class DOMAIN_RELIABILITY_EXPORT DomainReliabilityScheduler {
   // first_beacon_time_ saved during uploads.  Restored if upload fails.
   base::TimeTicks old_first_beacon_time_;
 
+  // Time until the next upload attempt on the last collector used. (Saved for
+  // histograms in Context.)
+  base::TimeDelta last_collector_retry_delay_;
+
   // Extra bits to return in GetWebUIData.
   base::TimeTicks scheduled_min_time_;
   base::TimeTicks scheduled_max_time_;