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

net/quic/platform/api/quic_clock.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_QUIC_PLATFORM_API_QUIC_CLOCK_H_
 #define NET_QUIC_PLATFORM_API_QUIC_CLOCK_H_
 
-#include "base/macros.h"
 #include "net/base/net_export.h"
 #include "net/quic/core/quic_time.h"
 
 namespace net {
 
-typedef double WallTime;
-
-// Clock to efficiently retrieve an approximately accurate time from an
-// EpollServer.
+// Interface for retreiving the current time.
 class NET_EXPORT_PRIVATE QuicClock {
  public:
   QuicClock();
   virtual ~QuicClock();
 
+  QuicClock(const QuicClock&) = delete;
+  QuicClock& operator=(const QuicClock&) = delete;
+
   // Returns the approximate current time as a QuicTime object.

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

Can you also define more precisely what "approximate" means, so that an impl
knows what to implement?

-  virtual QuicTime ApproximateNow() const;
+  virtual QuicTime ApproximateNow() const = 0;
 
   // Returns the current time as a QuicTime object.
   // Note: this use significant resources please use only if needed.

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

This note should probably say "this may use significant resources". 

-  virtual QuicTime Now() const;
+  virtual QuicTime Now() const = 0;
 
   // WallNow returns the current wall-time - a time that is consistent across
   // different clocks.
-  virtual QuicWallTime WallNow() const;
+  virtual QuicWallTime WallNow() const = 0;
 
   // Converts |walltime| to a QuicTime relative to this clock's epoch.
   virtual QuicTime ConvertWallTimeToQuicTime(
       const QuicWallTime& walltime) const;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(QuicClock);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_PLATFORM_API_QUIC_CLOCK_H_