Add a QuicChromiumClock and make QuicClock abstract to match internal code.

net/quic/platform/api/quic_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/platform/api/quic_clock.h"
 
-#include "base/time/time.h"
-
 namespace net {
 
 QuicClock::QuicClock() {}
 
 QuicClock::~QuicClock() {}
 
-QuicTime QuicClock::ApproximateNow() const {
-  // At the moment, Chrome does not have a distinct notion of ApproximateNow().
-  // We should consider implementing this using MessageLoop::recent_time_.
-  return Now();
-}
-
-QuicTime QuicClock::Now() const {
-  return QuicTime(base::TimeTicks::Now());
-}
-
-QuicWallTime QuicClock::WallNow() const {
-  return QuicWallTime::FromUNIXMicroseconds(base::Time::Now().ToJavaTime() *
-                                            1000);
-}
-
 QuicTime QuicClock::ConvertWallTimeToQuicTime(

[Jana, 2016/12/03 19:32:19]

Since all methods except for this one are pure virtual, I'm tempted to try and
make QuicClock an Interface class...  you make this method a utility method
outside of QuicClock, and make this class QuicClockInterface?

     const QuicWallTime& walltime) const {
   //     ..........................
   //     |            |           |
   // unix epoch   |walltime|   WallNow()
   //     ..........................
   //            |     |           |
   //     clock epoch  |         Now()
   //               result
   //
   // result = Now() - (WallNow() - walltime)
   return Now() - QuicTime::Delta::FromMicroseconds(
                      WallNow()
                          .Subtract(QuicTime::Delta::FromMicroseconds(
                              walltime.ToUNIXMicroseconds()))
                          .ToUNIXMicroseconds());
 }
 
 }  // namespace net