Allow backoff entry serialization if clock is null.

net/base/backoff_entry.cc

Index: net/base/backoff_entry.cc
diff --git a/net/base/backoff_entry.cc b/net/base/backoff_entry.cc
index 64125721c57f92f850b790b686986f6725825b63..a77c5251c9e647bba85748d36a4cb4fe9664c9c6 100644
--- a/net/base/backoff_entry.cc
+++ b/net/base/backoff_entry.cc
@@ -114,6 +114,10 @@ void BackoffEntry::Reset() {
   exponential_backoff_release_time_ = base::TimeTicks();
 }
 
+base::TimeTicks BackoffEntry::GetTimeTicksNow() const {
+  return clock_ ? clock_->NowTicks() : base::TimeTicks::Now();
+}
+
 base::TimeTicks BackoffEntry::CalculateReleaseTime() const {
   int effective_failure_count =
       std::max(0, failure_count_ - policy_->num_errors_to_ignore);
@@ -179,8 +183,4 @@ base::TimeTicks BackoffEntry::BackoffDurationToReleaseTime(
   return base::TimeTicks() + base::TimeDelta::FromMicroseconds(release_time_us);
 }
 
-base::TimeTicks BackoffEntry::GetTimeTicksNow() const {
-  return clock_ ? clock_->NowTicks() : base::TimeTicks::Now();
-}
-
 }  // namespace net