Reporting: Implement garbage collector.

net/reporting/reporting_policy.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_REPORTING_REPORTING_POLICY_H_
 #define NET_REPORTING_REPORTING_POLICY_H_
 
 #include "base/time/time.h"
 #include "net/base/backoff_entry.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 // Various policy knobs for the Reporting system.
 struct NET_EXPORT ReportingPolicy {
   // Provides a reasonable default for use in a browser embedder.
   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
 
 #endif  // NET_REPORTING_REPORTING_POLICY_H_