Reporting: Implement garbage collector.

net/reporting/reporting_policy.h

Index: net/reporting/reporting_policy.h
diff --git a/net/reporting/reporting_policy.h b/net/reporting/reporting_policy.h
index 5f472d7fe5edbaf971d1f243cafea2a8e2be143f..0cc31f9fdcef04192e64c2bee4f3047817249d8c 100644
--- a/net/reporting/reporting_policy.h
+++ b/net/reporting/reporting_policy.h
@@ -18,8 +18,18 @@ struct NET_EXPORT ReportingPolicy {
   ReportingPolicy(const ReportingPolicy& other);
   ~ReportingPolicy();
 
+  // Maximum age a report can be queued for before being discarded as expired.
+  base::TimeDelta max_report_age;
+
+  // Maximum number of delivery attempts a report can have before being
+  // discarded as failed.
+  int max_report_attempts;
+
   // Backoff policy for failing endpoints.
   BackoffEntry::Policy endpoint_backoff_policy;
+
+  // Minimum interval at which to garbage-collect the cache.
+  base::TimeDelta garbage_collection_interval;
 };
 
 }  // namespace net