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

net/quic/platform/impl/quic_chromium_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/impl/quic_chromium_clock.h"
+
+#include "base/time/time.h"
+
+namespace net {
+
+QuicChromiumClock::QuicChromiumClock() {}
+
+QuicChromiumClock::~QuicChromiumClock() {}
+
+QuicTime QuicChromiumClock::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 QuicChromiumClock::Now() const {
+  return QuicTime(base::TimeTicks::Now());
+}
+
+QuicWallTime QuicChromiumClock::WallNow() const {
+  return QuicWallTime::FromUNIXMicroseconds(base::Time::Now().ToJavaTime() *
+                                            1000);
+}
+
+}  // namespace net