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

net/quic/platform/impl/quic_chromium_clock.h

Index: net/quic/platform/impl/quic_chromium_clock.h
diff --git a/net/quic/platform/impl/quic_chromium_clock.h b/net/quic/platform/impl/quic_chromium_clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..e703f246cfb5e71beee97b2d51f3043840f111e7
--- /dev/null
+++ b/net/quic/platform/impl/quic_chromium_clock.h
@@ -0,0 +1,31 @@
+// 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_IMPL_QUIC_CHROMIUM_CLOCK_H_
+#define NET_QUIC_PLATFORM_IMPL_QUIC_CHROMIUM_CLOCK_H_
+
+#include "base/time/time.h"
+#include "net/quic/platform/api/quic_clock.h"
+
+namespace net {
+
+// Clock to efficiently retrieve an approximately accurate time from an
+// EpollServer.
+class NET_EXPORT_PRIVATE QuicChromiumClock : public QuicClock {
+ public:
+  QuicChromiumClock();
+  ~QuicChromiumClock() override;
+
+  // QuicClock implementation:
+  QuicTime ApproximateNow() const override;
+  QuicTime Now() const override;
+  QuicWallTime WallNow() const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(QuicChromiumClock);
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_PLATFORM_IMPL_QUIC_CHROMIUM_CLOCK_H_