MockClock needs to mock the NowAsDeltaSinceUnixEpoch method.

net/quic/test_tools/mock_clock.cc

 // 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.
 
 #include "net/quic/test_tools/mock_clock.h"
 
 namespace net {
 
 MockClock::MockClock() {
 }
 
 MockClock::~MockClock() {
 }
 
 void MockClock::AdvanceTime(QuicTime::Delta delta) {
   CHECK_LE(0, delta.ToMicroseconds());
   now_ = now_.Add(delta);
 }
 
 QuicTime MockClock::Now() const {
   return now_;
 }
 
+QuicTime::Delta MockClock::NowAsDeltaSinceUnixEpoch() const {
+  return now_.Subtract(QuicTime());
+}
+
 base::TimeTicks MockClock::NowInTicks() const {
   base::TimeTicks ticks;
   return ticks + base::TimeDelta::FromMicroseconds(
       now_.Subtract(QuicTime()).ToMicroseconds());
 }
 
 }  // namespace net