Reporting: Implement garbage collector.

net/reporting/reporting_garbage_collector.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_GARBAGE_COLLECTOR_H_
+#define NET_REPORTING_REPORTING_GARBAGE_COLLECTOR_H_
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+class ReportingCache;
+
+// Removes reports that have remained undelivered for too long or that have been
+// included in too many failed delivery attempts. Also, removes reports on
+// network changes, if so configured.
+class NET_EXPORT ReportingGarbageCollector {

[Randy Smith (Not in Mondays), 2017/03/31 15:36:55]

Why this design?  What you've effectively got here is a namespace wrapping a
function that something else has to call every once in a while.  Why not
construct a singleton (which, yes, something else has to own, but can own and
forget until teardown) which decides how often it needs to wakeup and GC, and
stores the policy (since that's presumably not going to change)?

+ public:
+  struct Policy {
+    // How long a report can remain undelivered before being GCed.
+    base::TimeDelta report_max_age;
+
+    // How many times delivery of a report can fail before the report will be
+    // GCed.
+    int report_max_attempts;
+
+    // Whether reports are allowed to persist across network changes.
+    bool report_persist_across_network_changes;
+  };
+
+  static void CollectGarbage(ReportingCache* cache,
+                             const Policy& policy,
+                             base::TimeTicks now,
+                             bool network_changed);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(ReportingGarbageCollector);
+};
+
+}  // namespace net
+
+#endif  // NET_REPORTING_REPORTING_GARBAGE_COLLECTOR_H_