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 8fcd2396430562752e4cc02510c66566475ee75d..b8dcf2440a34d17a49c06cffdecf408d39eaafb7 100644
--- a/components/domain_reliability/scheduler.h
+++ b/components/domain_reliability/scheduler.h
@@ -82,6 +82,13 @@ class DOMAIN_RELIABILITY_EXPORT DomainReliabilityScheduler {
   // uploaded.
   base::TimeTicks first_beacon_time() const { return first_beacon_time_; }
 
+  // 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();
 
@@ -119,6 +126,10 @@ 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_;