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"
@@ skipping 90 matching lines @@
   // just as well start with a fresh BackoffEntry object), and hasn't
   // had for Policy::entry_lifetime_ms.
   bool CanDiscard() const;
 
   // Resets this entry to a fresh (as if just constructed) state.
   void Reset();
 
   // Returns the failure count for this entry.
   int failure_count() const { return failure_count_; }
 
-  // Returns the TickClock passed in to the constructor. May be NULL.
-  base::TickClock* tick_clock() const { return clock_; }
+  // Equivalent to TimeTicks::Now(), using clock_ if provided.
+  base::TimeTicks GetTimeTicksNow() const;
 
  private:
   // Calculates when requests should again be allowed through.
   base::TimeTicks CalculateReleaseTime() const;
 
-  // Equivalent to TimeTicks::Now(), using clock_ if provided.
-  base::TimeTicks GetTimeTicksNow() const;
-
   // Timestamp calculated by the exponential back-off algorithm at which we are
   // allowed to start sending requests again.
   base::TimeTicks exponential_backoff_release_time_;
 
   // Counts request errors; decremented on success.
   int failure_count_;
 
   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_