Change to calculate the real NTP in TimeTicks.

media/cast/cast_ntp_tick_clock.h

+// Copyright 2013 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 MEDIA_CAST_CAST_NTP_TICK_CLOCK_H_
+#define MEDIA_CAST_CAST_NTP_TICK_CLOCK_H_
+
+#include "base/basictypes.h"
+#include "base/time/default_tick_clock.h"
+#include "base/time/tick_clock.h"
+#include "base/time/time.h"
+#include "media/cast/cast_defines.h"
+
+namespace media {
+namespace cast {
+
+// Class that provide the a TickTime relative to NTP. The base TickTime does not
+// reference a specific date. This version is number of ticks relative to 0h UTC
+// on 1 January 1900.
+// Note: We only synchronize with the system clock at creation time after that
+// we only use our relative difference this can result in a drift relative to
+// the system clock however this approach guarantees that out NTP time never
+// decrease (if the user changes the computer clock, Time::Now() may actually
+// decrease or jump).
+
+class CastNtpTickClock : public base::TickClock {
+ public:
+  CastNtpTickClock();
+  virtual ~CastNtpTickClock();
+
+  virtual base::TimeTicks NowTicks() OVERRIDE;
+
+ protected:
+  // Provided for testability.
+  void SetTickClock(base::TickClock* tick_clock);
+
+ private:
+  base::DefaultTickClock default_tick_clock_;
+  base::TickClock* tick_clock_;
+  base::TimeDelta start_offset_;
+
+  DISALLOW_COPY_AND_ASSIGN(CastNtpTickClock);
+};
+
+}  // namespace cast
+}  // namespace media
+
+#endif  // MEDIA_CAST_CAST_NTP_TICK_CLOCK_H_
+
+