Allow BackoffEntry to be serialized and deserialized.

net/base/backoff_entry_serializer.h

+// Copyright 2015 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_BASE_BACKOFF_ENTRY_SERIALIZER_H_
+#define NET_BASE_BACKOFF_ENTRY_SERIALIZER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+#include "net/base/backoff_entry.h"
+#include "net/base/net_export.h"
+
+namespace base {
+class ListValue;
+class TickClock;
+}
+
+namespace net {
+
+// Serialize or deserialize a BackoffEntry, so it can persist beyond the
+// lifetime of the browser.
+class NET_EXPORT BackoffEntrySerializer {
+ public:
+  // Serializes the release time and failure count into a ListValue that can
+  // later be passed to Deserialize to re-create the given BackoffEntry. The
+  // Policy is not serialized, instead callers must pass an identical Policy*
+  // when deserializing. |time_now| should be base::Time::Now(), except for
+  // tests that want to simulate time changes. The release time TimeTicks will
+  // be converted to an absolute timestamp, thus the time will continue counting
+  // down even whilst the device is powered off, and will be partially
+  // vulnerable to changes in the system clock time.
+  static scoped_ptr<base::ListValue> SerializeToValue(const BackoffEntry& entry,
+                                                      base::Time time_now);
+
+  // Deserializes a ListValue back to a BackoffEntry. |policy| MUST be the same
+  // Policy as the serialized entry had. |clock| may be null. Both |policy| and
+  // |clock| (if not null) must enclose lifetime of the returned BackoffEntry.
+  // |time_now| should be base::Time::Now(), except for tests that want to
+  // simulate time changes. The absolute timestamp that was serialized will be
+  // converted back to TimeTicks as best as possible. Returns null if
+  // deserialization was unsuccessful.

[mmenke, 2015/05/06 17:34:48]

nit:  NULL is generally capitalized in net/ when it refers to a NULL pointer.

[johnme, 2015/05/06 20:38:08]

Done (I'd stopped doing this with C++11, as it's usually nullptr rather than the
NULL macro. But happy to keep consistent with net/).

+  static scoped_ptr<BackoffEntry> DeserializeFromValue(
+      const base::ListValue& serialized,

[mmenke, 2015/05/06 17:34:48]

Suggest base::Value here and above.  Consumer probably shouldn't have to know or
care what type of value it is.  I assume there's no storage API you plan to use
that demands list values, so this also makes it a little simpler on consumers -
won't have to get a pointer to serialized as a ListValue, starting from a Value.

[johnme, 2015/05/06 20:38:08]

Done.

+      const BackoffEntry::Policy* policy,
+      base::TickClock* clock,
+      base::Time time_now);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(BackoffEntrySerializer);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_BACKOFF_ENTRY_SERIALIZER_H_