Allow backoff entry serialization if clock is null.

net/base/backoff_entry.h

 // Copyright (c) 2012 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_H_
 #define NET_BASE_BACKOFF_ENTRY_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time/time.h"
 #include "net/base/net_export.h"
 
 namespace base {
 class TickClock;
 }
 
 namespace net {
 
 // Provides the core logic needed for randomized exponential back-off
 // on requests to a given resource, given a back-off policy.
 //
 // This utility class knows nothing about network specifics; it is
 // intended for reuse in various networking scenarios.
 class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+  friend class BackoffEntrySerializer;

[johnme, 2016/10/03 12:18:22]

Reviewers in https://codereview.chromium.org/1023473003#msg13 had a preference
for avoiding friend classes unless really needed. It might make sense to make
GetTimeTicksNow() public instead of friending? Alternatively, if you do make
BackoffEntrySerializer a friend class, you should probably make
BackoffDurationToReleaseTime private (it's only currently public so
BackoffEntrySerializer can use it).

[Olivier, 2016/10/03 12:29:24]

Done.

+
  public:
   // The set of parameters that define a back-off policy. When modifying this,
   // increment SERIALIZATION_VERSION_NUMBER in backoff_entry_serializer.cc.
   struct Policy {
     // Number of initial errors (in sequence) to ignore before applying
     // exponential back-off rules.
     int num_errors_to_ignore;
 
     // Initial delay.  The interpretation of this value depends on
     // always_use_initial_delay.  It's either how long we wait between
@@ skipping 91 matching lines @@
   const Policy* const policy_;  // Not owned.
 
   base::TickClock* const clock_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_BACKOFF_ENTRY_H_